Replace progress bar in director ychooser with an animation + add control to abort folder scanning.

[Oliver-Loeffler]

The directory chooser indicates folder scanning by using a shrinked progress bar.
An animation (e.g. jumping / pumping directory icon or an icon with a loupe, rotating etc.) would be a better match.

Also as of now one can abort folder scanning but this is only indicated by a tool tip. It would be better to create a red cross etc. or another more clear indication.