Support for Storage Access Framework

* EntryEditActivity: support content-URIs and extracting display names from them
* AndroidContentStorage.cs, SelectStorageLocationActivityBase.cs: support for SAF with persistable URI permissions
* FileChooser returns URI as data
* CreateDatabaseActivity.cs supports content URIs
* FileStorageSelectionActivity: doesn't show "Local file" anymore, now system file picker on KitKat

src/Kp2aUnitTests/TestSelectStorageLocation.cs

@@ -328,7 +328,7 @@ namespace Kp2aUnitTests
 			}
 		}
 
-		protected override void ShowAndroidBrowseDialog(int requestCode, bool isForSave)
+		protected override void ShowAndroidBrowseDialog(int requestCode, bool isForSave, bool tryGetPermanentAccess)
 		{
 			_userAction = new AndroidBrowseDialogAction(requestCode, isForSave, this);
 		}