Is your suggestion for improvement related to a problem? Please describe.
Currently, no progress or indication of the background index creation is shown. This may irritate some users because they may think that there is a performance bug in jabref due to the high usage of resources.

Describe the solution you'd like
Show an indicator of the progress (how many files to go etc) in the progress icon in the upper right corner of the screen.

@btut @koppor @calixtus