Skin Layers 3D

This update mainly targets performance:

- In the default settings, rendering of the skin layers should be about 2 times faster

- Added a setting to disable fast render, it will prevent some visual issues with transparency at the cost of performance(still faster than the 1.3.0 release), requires a relog into the world/server

- Fixed small memory leak (Thanks coderbot16)

- Head and body mesh will get built at the same time, reducing stutter