Fix clone volume UI for filtering files

[mzur]

If a volume should be cloned and the user wants to filter the files, it is necessary to press Enter in the filename filter input field so BIIGLE loads the list of files. If Enter is not pressed, no filtering will be done even if the input is filled.

The UI should be improved as follows:

1. When the filter input is filled, replace the "clone" button with a "test file query" button
2. The user has to press this button first and view the preview of filtered files
3. After the filtered files are displayed, the "clone" button appears again and can be pressed
4. If the filter query changes, start again at 1.

This will ensure that the clone button is pressed only after the list of filtered files was loaded.