Use separate crate to compile anim as a cdylib to avoid compiling both all the time and improve voxygen pipelining

• Also fixes thread builder usage so voxygen hot-anim feature compiles (I guess no one has merged a fix for this yet?)
• Also make things work from the root repo dir in addition to voxygen's dir

anim crate can start compiling much earlier and thus voxygen can as well:

• By opening this merge request, you agree to release your code and all other changes under the GPL 3 license and to abide by the terms set by this license.
• Migrations have been added if applicable
• Significant changes of this merge request have been added to the changelog.