Customizable Player Models

Ported to Minecraft 1.19.3
Added 'Remove Bed Offset' effect to fix a vanilla bug (Closes #296)

Fixed animations dropdown not updating correctly
Fixed the creative flying animation overwriting the riding animation
Fixed staged animations not playing when setup animation is missing
Fixed display menu not displaying the correct state for some checkboxes
Fixed some crashes (Closes #322)
Internal cleanup
Added plugin message system for the API