Remove unused textures/flats checks ANIMATED and SWITCHES lumps for animation frames

[AureliusGit]

trafficstars

To reduce manual work, the maintenance tool for removing unused textures/flats could check the ANIMATED and SWITCHES lumps for animation frames, so that they wouldn't need to be manually checked out. In other words, if even one animation frame is used in the map, all of the frames of that particular animation would be automatically unchecked and therefore not deleted.

[sirjuddington]

This one is kind of a duplicate of #842 but that one doesn't mention SWITCHES so I'll keep this one open for now

[XaserAcheron]

Bump from the future! D:

Reviving this -- This is coming up a lot more often lately because of OTEX -- people are copying the entirety of the texture pack (all zillion megabytes of it) to their wad since SLADE's prune function breaks its animations & switches.

In general, there currently is no community-accepted answer for "how do I remove unused textures?", since you can't easily do it manually, DoomTools' features are (currently) limited to power users, and people are scared of SLADE's feature because of this and related issues (lack of MAPINFO sky support).