Support stack-based effect pushing / popping in the render context

Summary:
Ref T246.

This updates Protogame to support:

  * Stack-based effect pushing / popping in the render context
  * Transparently reloading assets in the local asset manager (using the same pattern that the network manager uses).

Test Plan: Updated Tychaia to work with the new code.

Reviewers: Sabre070

Reviewed By: Sabre070

Maniphest Tasks: T246

Differential Revision: https://code.redpointsoftware.com.au/D139