Renderer refactor

[eulertour]

This PR addresses some of #524.

• Creates a CairoRenderer class containing all of the frame handling / caching / skipping logic previously done in Scene
• Removed test_camera.py and added test_renderer.py (which does the same thing)
• Updated references to Scene.camera to Scene.renderer.camera, likewise for Scene.file_writer

There is still more work to be done here.

• The CairoRenderer can't be instantiated without passing it a Scene first, i.e. the following is impossible:

renderer = CairoRenderer() if args.use_cairo else JsRenderer()
scene = SceneClass(renderer)

• There are still references to the Scene in the SceneFileWriter
• The variants of the Camera class still need to removed in favor of a more general one
• The current Camera class should either be renamed into something like FrameBuilder or absorbed into the CairoRenderer that holds it

[huguesdevimeux]

Some comments :D

[eulertour]

@huguesdevimeux Why did you mark this as a draft?

[huguesdevimeux]

Because you said it is WIP, isn't it ?

[eulertour]

It addresses part of the issue from #524 but I'd rather fix that issue gradually to keep the PRs small and avoid having to continually rebase.

[huguesdevimeux]

I'm sorry then.

I unmarked it

I thought I left comments and not approved, it appears that I missclicked. Sorry for that

[leotrs]

This LGTM in general. I haven't reviewed every single line because most of it looks like refactoring and moving stuff around and simplifying logic. That and the tests pass, so it's all good.

[behackl]

I really like how this cleans up the mess in scene/scene.py by really a lot. Thank you very much for your efforts!

I just added a few suggestions here and there (most of them concerning unused imports), but none of them are actually blocking. Feel free to handle them in any way you like.