Add JSch (SFTP) debug logging

-App Settings->Log-File for Debugging->SFTP debug logging
-Logs to android log (logcat) if log file is not enabled
-Logs to Kp2a log file if it is enabled
-Logs are tagged as "KP2AJFS[JSch]"
-When enabled, logs ALL levels (DEBUG+).

NOTE: Sensitive SSH connection information may be logged!!

src/KeePassLib2Android/Kp2aLog.cs

@@ -58,12 +58,12 @@ namespace keepass2android
 
 		}
 
-		private static string LogFilename
+		public static string LogFilename
 		{
 			get { return Application.Context.FilesDir.CanonicalPath +"/keepass2android.log"; }
 		}
 
-		private static bool LogToFile
+		public static bool LogToFile
 		{
 			get
 			{