Make animations configurable and compositable

[oversword]

This is basically a re-write and should be taken as a suggestion, I understand if the creators don't want the mod to be taken in this direction.

This was all done to facilitate a new sneak animation I want to implement, instead of just adding a new animation for every combination (like walk_mine does) we should make all animations independent so they can be combined in any way you like.

Features:

• Allow multiple animations at once by compositing them
• Allow users to register their own animations
• Allow users to assign animations to players
• Allow the speed of the animation to be set
• Allow rotation on sneak to be disabled

Changes:

• Add a global for the mod to provide an API for users to configure their own animations
• Move all localisation of helper functions to one place
• Change all animations to modify only the parts of the model they affect
• Move looking head and lagging body to options in the animation registration
• Change model files to have clear separation of the bones and the specific animation settings
• Re-write the main function to allow for all of this