Shapekey Update to meshtools.py

[TheDarkFleet]

Added functionality to allow modifiers to be applied to meshes and shapekeys rebuilt.

This will not play nicely with the refit check as it currently stands, and will allow a user to apply the refit endlessly (this can be hilarious, but not ideal).

(Probably not an ideal implementation, but its worked for me)

[DoctorPresto]

Thanks for the PR! Whenever I get home tonight I'll take a proper look at this

[DoctorPresto]

Looking quickly I'm not really a fan of this implementation. The better/easier route is to apply the modifier as a shapekey, set garment support and the refit shapekey to 1, make a new shapekey from the mix then to delete basis + garment support so that the refit shapekey becomes the new basis and the mix shapekey becomes the new garment support

[TheDarkFleet]

There are probably better ways to get the same result, I've just been doing it this way for a while now and thought to share it in case it helped anyone else out as I know a few people have talked about doing this manually being quite tedious.

[DoctorPresto]

feature added with suggested implementation