Per entity/collider debug rendering

[barsoosayque]

I needed a way to toggle debug rendering of colliders for group of entities in my project, so I thought of implementing it kind of like bevy Wireframe works, with global flag in resource, and if it's off, then per entity with marker component. I also considered just using Visibility for collider entities, but that's seems unintuitive.

~Oh, I also fixed RapierDebugRenderPlugin::enabled not being used, I'm not sure if creating context with enabled: true was intentional or just a typo.~ (fixed in recent master)