Draft: Split player model animations into separate files

Closes #14

Sample video about the enhancement of the new animations for player models before MR:
https://streamable.com/iyd0uk

Added Blender script to remove all Xonotic player model animation actions to start from scratch for every model.
There's a .framegroups file used to help the player animations, remember this file cannot be modified!

Old player models, no longer used, will be moved in a folder called old_models soon.