Migrate to PixiJS/WebGL

Right now a lot of the "engine" is based on Javascript 'ticks', which are single-threaded, unreliable, and unperformant.

We can migrate the 'tick' and scheduling mechanisms to https://pixijs.com/ which has it's own dedicated process thread in browsers. This will be better for larger groups of users.

Start by locating the engine’s JavaScript tick and scheduling mechanisms. Then determine how the proposed PixiJS/WebGL migration fits the existing architecture; done means those mechanisms use PixiJS and support larger groups of users reliably.

Written by the indexing model from the issue text.