[FEATURE] - Powerpoint file support.

[michaeljharrison]

Is your feature request related to a problem? Please describe.
Powerpoint files currently show as generic files are don't have thumbnails or previews.

Describe the solution you'd like
Thumbnails and full previews for powerpoint files.

Describe alternatives you've considered
At least specific handling and marking of powerpoint files.

Additional context
Add any other context or screenshots about the feature request here.