don't show some menu items when viewing history elements, closes #2967

Update Jsch and switch to maven dependency. This adds more recent algorithms to the SFTP implementation and improves maintainability.

src/keepass2android-app/EntryActivity.cs

@@ -1350,7 +1350,16 @@ namespace keepass2android
 		public override bool OnPrepareOptionsMenu(IMenu menu)
 		{
 			Util.PrepareDonateOptionMenu(menu, this);
-			return base.OnPrepareOptionsMenu(menu);
+
+			// hide the move and delete options if we're viewing a history element. It is not clear 
+			// what the option then means.
+			foreach (var id in new List<int>{Resource.Id.menu_move, Resource.Id.menu_delete})
+            {
+                var menuItem = menu.FindItem(id);
+                menuItem?.SetVisible(_historyIndex < 0);
+            }
+
+            return base.OnPrepareOptionsMenu(menu);
 		}
 
 		bool isPaused = false;