add some info texts, especialy for novice users to avoid some common misunderstandings. closes #46, closes #47

src/Kp2aBusinessLogic/Io/AndroidContentStorage.cs

@@ -28,7 +28,12 @@ namespace keepass2android.Io
 			get { yield return "content"; }
 		}
 
-		public void Delete(IOConnectionInfo ioc)
+	    public bool UserShouldBackup
+	    {
+	        get { return true; }
+	    }
+
+	    public void Delete(IOConnectionInfo ioc)
 		{
 			throw new NotImplementedException();
 		}

src/Kp2aBusinessLogic/Io/BuiltInFileStorage.cs

@@ -59,7 +59,12 @@ namespace keepass2android.Io
 
 		public abstract IEnumerable<string> SupportedProtocols { get; }
 
-		public void Delete(IOConnectionInfo ioc)
+	    public bool UserShouldBackup
+	    {
+	        get { return true; }
+	    }
+
+	    public void Delete(IOConnectionInfo ioc)
 		{
 			//todo check if directory
 			IOConnection.DeleteFile(ioc);

src/Kp2aBusinessLogic/Io/CachingFileStorage.cs

@@ -84,7 +84,12 @@ namespace keepass2android.Io
 
 		public IEnumerable<string> SupportedProtocols { get { return _cachedStorage.SupportedProtocols; } }
 
-		public void DeleteFile(IOConnectionInfo ioc)
+	    public bool UserShouldBackup
+	    {
+	        get { return _cachedStorage.UserShouldBackup; }
+	    }
+
+	    public void DeleteFile(IOConnectionInfo ioc)
 		{
 			if (IsCached(ioc))
 			{

src/Kp2aBusinessLogic/Io/DropboxFileStorage.cs

@@ -10,7 +10,11 @@ namespace keepass2android.Io
 		{
 		}
 
-		
+
+	    public override bool UserShouldBackup
+	    {
+	        get { return false; }
+	    }
 	}
 
 	public partial class DropboxAppFolderFileStorage: JavaFileStorage
@@ -20,8 +24,12 @@ namespace keepass2android.Io
 		{
 		}
 
-		
-	}
+	    public override bool UserShouldBackup
+	    {
+	        get { return false; }
+	    }
+
+    }
 	
 }
 #endif

src/Kp2aBusinessLogic/Io/GDriveFileStorage.cs

@@ -22,6 +22,10 @@ namespace keepass2android.Io
 		}
 
 
+	    public override bool UserShouldBackup
+	    {
+	        get { return false; }
+	    }
 	}
 }
 #endif

src/Kp2aBusinessLogic/Io/IFileStorage.cs

@@ -46,9 +46,14 @@ namespace keepass2android.Io
 		/// <summary>
 		/// returns the protocol ids supported by this FileStorage. Can return pseudo-protocols like "dropbox" or real protocols like "ftp"
 		/// </summary>
-		IEnumerable<string> SupportedProtocols { get; } 
+		IEnumerable<string> SupportedProtocols { get; }
 
-		/// <summary>
+        /// <summary>
+        /// returns true if users should backup files on this file storage (if the file is important). Can be false for cloud providers with built-in versioning or backups.
+        /// </summary>
+	    bool UserShouldBackup { get; }
+
+	    /// <summary>
 		/// Deletes the given file or directory.
 		/// </summary>
 		void Delete(IOConnectionInfo ioc);

src/Kp2aBusinessLogic/Io/JavaFileStorage.cs

@@ -22,9 +22,10 @@ namespace keepass2android.Io
 		protected string Protocol { get { return _jfs.ProtocolId; } }
 
 		public virtual IEnumerable<string> SupportedProtocols { get { yield return Protocol; } }
+	    public abstract bool UserShouldBackup { get; }
 
 
-		private readonly IJavaFileStorage _jfs;
+	    private readonly IJavaFileStorage _jfs;
 		private readonly IKp2aApp _app;
 
 		public JavaFileStorage(IJavaFileStorage jfs, IKp2aApp app)

src/Kp2aBusinessLogic/Io/NetFtpFileStorage.cs

@@ -161,7 +161,12 @@ namespace keepass2android.Io
 			}
 		}
 
-		public void Delete(IOConnectionInfo ioc)
+	    public bool UserShouldBackup
+	    {
+	        get { return true; }
+	    }
+
+	    public void Delete(IOConnectionInfo ioc)
 		{
 			try
 			{

src/Kp2aBusinessLogic/Io/OfflineSwitchableFileStorage.cs

@@ -32,7 +32,12 @@ namespace keepass2android.Io
 			get { return _baseStorage.SupportedProtocols; }
 		}
 
-		public void Delete(IOConnectionInfo ioc)
+	    public bool UserShouldBackup
+	    {
+	        get { return _baseStorage.UserShouldBackup; }
+	    }
+
+	    public void Delete(IOConnectionInfo ioc)
 		{
 			_baseStorage.Delete(ioc);
 		}

src/Kp2aBusinessLogic/Io/OneDriveFileStorage.cs

@@ -33,6 +33,11 @@ namespace keepass2android.Io
 				yield return "onedrive";
 			}
 		}
+
+	    public override bool UserShouldBackup
+	    {
+	        get { return false; }
+	    }
 	}
 }
 #endif

src/Kp2aBusinessLogic/Io/SftpFileStorage.cs

@@ -10,7 +10,11 @@ namespace keepass2android.Io
 		{
 		}
 
-		
+
+	    public override bool UserShouldBackup
+	    {
+	        get { return true; }
+	    }
 	}
 
 	

src/Kp2aBusinessLogic/Io/WebDavFileStorage.cs

@@ -33,7 +33,12 @@ namespace keepass2android.Io
 			}
 		}
 
-		public static string Owncloud2Webdav(string owncloudUrl)
+	    public override bool UserShouldBackup
+	    {
+	        get { return true; }
+	    }
+
+	    public static string Owncloud2Webdav(string owncloudUrl)
 		{
 			string owncloudPrefix = "owncloud://";
 			if (owncloudUrl.StartsWith(owncloudPrefix))