Implement application backend for yage-web

Implement a framework in yage-web for running yage in a web browser.
It should be reusable in a way that an actual application using it would be as small as possible (abstract things away, if possible).

It must adhere to the rendering structure, so e.g. there must be an instance of Canvas somewhere. The backend controls the mainloop in the wait that is necessary in the browser, and it then passes on control to the Canvas. This does not need to be as flexible as in the native case - it only needs to meet the assumptions of the rendering interface. For example, update and render does not need to be separated - they can always be called together, which should fit requestAnimationFrame.

Start by locating the yage-web rendering interface and the Canvas entry point, then trace how the native backend structures its main loop. Define the browser backend around requestAnimationFrame while preserving the rendering structure and passing control to a Canvas. Done means an application can use the reusable framework with minimal setup and the browser rendering loop works.

Written by the indexing model from the issue text.