* Introduced IFileStorage interface: Better abstraction than current IOConnection (suitable for cloud support). Currently only implemented by the built-in IOConnection (local/http/ftp)

* Implemented Merge functionality for SaveDB. UI is not yet implemented!
* Added tests for merge functionality

src/Kp2aBusinessLogic/Io/BuiltInFileStorage.cs

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+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+using Android.App;
+using Android.Content;
+using Android.OS;
+using Android.Runtime;
+using Android.Views;
+using Android.Widget;
+using KeePassLib.Serialization;
+using KeePassLib.Utility;
+
+namespace keepass2android.Io
+{
+	public class BuiltInFileStorage: IFileStorage
+	{
+		public void DeleteFile(IOConnectionInfo ioc)
+		{
+			IOConnection.DeleteFile(ioc);
+		}
+
+		public bool CheckForFileChangeFast(IOConnectionInfo ioc, string previousFileVersion)
+		{
+			if (!ioc.IsLocalFile())
+				return false;
+			DateTime previousDate;
+			if (!DateTime.TryParse(previousFileVersion, out previousDate))
+				return false;
+			return File.GetLastWriteTimeUtc(ioc.Path) > previousDate;
+		}
+
+		
+		public string GetCurrentFileVersionFast(IOConnectionInfo ioc)
+		{
+
+			if (ioc.IsLocalFile())
+			{
+				return File.GetLastWriteTimeUtc(ioc.Path).ToString(CultureInfo.InvariantCulture);
+			}
+			else
+			{
+				return DateTime.MinValue.ToString(CultureInfo.InvariantCulture);
+			}
+
+
+		}
+
+		public Stream OpenFileForRead(IOConnectionInfo ioc)
+		{
+			return IOConnection.OpenRead(ioc);
+		}
+
+		public IWriteTransaction OpenWriteTransaction(IOConnectionInfo ioc, bool useFileTransaction)
+		{
+			return new BuiltInFileTransaction(ioc, useFileTransaction);
+		}
+
+		public class BuiltInFileTransaction : IWriteTransaction
+		{
+			private readonly FileTransactionEx _transaction;
+
+			public BuiltInFileTransaction(IOConnectionInfo ioc, bool useFileTransaction)
+			{
+				_transaction = new FileTransactionEx(ioc, useFileTransaction);
+			}
+
+			public void Dispose()
+			{
+				
+			}
+
+			public Stream OpenFile()
+			{
+				return _transaction.OpenWrite();
+			}
+
+			public void CommitWrite()
+			{
+				_transaction.CommitWrite();
+			}
+		}
+
+		public bool CompleteIoId()
+		{
+			throw new NotImplementedException();
+		}
+
+		public bool? FileExists()
+		{
+			throw new NotImplementedException();
+		}
+
+		public string GetFilenameWithoutPathAndExt(IOConnectionInfo ioc)
+		{
+			return UrlUtil.StripExtension(
+				UrlUtil.GetFileName(ioc.Path));
+
+		}
+	}
+}

src/Kp2aBusinessLogic/Io/IFileStorage.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+
+using Android.App;
+using Android.Content;
+using Android.OS;
+using Android.Runtime;
+using Android.Views;
+using Android.Widget;
+using KeePassLib.Keys;
+using KeePassLib.Serialization;
+
+namespace keepass2android.Io
+{
+	/// <summary>
+	/// Called as a callback from CheckForFileChangeAsync.
+	/// </summary>
+	/// <param name="ioc"></param>
+	/// <param name="fileChanged"></param>
+	public delegate void OnCheckForFileChangeCompleted(IOConnectionInfo ioc, bool fileChanged);
+
+	/// <summary>
+	/// Interface to encapsulate all access to disk or cloud.
+	/// </summary>
+	/// This interface might be implemented for different cloud storage providers in the future to extend the possibilities of the
+	/// "built-in" IOConnection class in the Keepass-Lib. 
+	/// Note that it was decided to use the IOConnectionInfo also for cloud storage (unless it turns out that this isn't possible, but 
+	/// with prefixes like dropbox:// it should be). The advantage is that the database for saving recent files etc. will then work without 
+	/// much work to do. Furthermore, the IOConnectionInfo seems generic info to capture all required data, even though it might be nicer to 
+	/// have an IIoStorageId interface in few cases.*/
+	public interface IFileStorage
+	{
+		/// <summary>
+		/// Deletes the given file.
+		/// </summary>
+		void DeleteFile(IOConnectionInfo ioc);
+
+		/// <summary>
+		/// Tests whether the file was changed. 
+		/// </summary>
+		/// Note: This function may return false even if the file might have changed. The function
+		/// should focus on being fast and cheap instead of doing things like hashing or downloading a full file.
+		/// <returns>Returns true if a change was detected, false otherwise.</returns>
+		bool CheckForFileChangeFast(IOConnectionInfo ioc , string previousFileVersion);
+
+		/// <summary>
+		/// Returns a string describing the "version" of the file specified by ioc.
+		/// </summary>
+		/// This string may have a deliberate value (except null) and should not be used by callers except for passing it to
+		/// CheckForFileChangeFast().
+		/// <returns>A string which should not be null.</returns>
+		string GetCurrentFileVersionFast(IOConnectionInfo ioc);
+
+		Stream OpenFileForRead(IOConnectionInfo ioc);
+		//Stream OpenFileForWrite( IOConnectionInfo ioc, bool useTransaction);
+		IWriteTransaction OpenWriteTransaction(IOConnectionInfo ioc, bool useFileTransaction);
+
+		/// <summary>
+		/// brings up a dialog to query credentials or something like this.
+		/// </summary>
+		/// <returns>true if success, false if error or cancelled by user</returns>
+		bool CompleteIoId( /*in/out ioId*/);
+
+
+		/// <summary>
+		/// Checks whether the given file exists.
+		/// </summary>
+		/// <returns>true if it exists, false if not. Null if the check couldn't be performed (e.g. because no credentials available or no connection established.)</returns>
+		bool? FileExists( /*ioId*/);
+
+		string GetFilenameWithoutPathAndExt(IOConnectionInfo ioc);
+	}
+
+	public interface IWriteTransaction: IDisposable
+	{
+		Stream OpenFile();
+		void CommitWrite();
+	}
+}