Improve filter generation speed

[steven-esser]

Currently when working with large scans with many clues, generating filter values can sometimes take a very long amount of time. The poor performance of filter generation ends up "locking" Aboutcode Manager, which is not a good user experience.

There are a few workarounds, but ultimately they are not proper solutions.

[steven-esser]

Some observations from @mjherzog:

It is a Fileinfo-only scan with 91,493 entries - 59,346 files.
It took 18 seconds to load existing SQLite file
It took 2 min 48 secs to Activate Filters (I added Type to the column set before activating)
These two processes seem very slow for file of this size and content, but I do not have a direct comp.