Higher-order components and helpers

[Izzimach]

Creating the various components (most notably <Scene> and <Mesh>) are pretty cumbersome even if you just want a simple scene with a single mesh in it. There are a lot of fiddly props and boilerplate that feels very Un-React-ish.

However, IMO the basic react-three components should try to mirror three.js as close as possible which makes it easier to maintain and test the components. A possible approach is to create a set of "higher-order components" which wrap the default components and add sensible defaults or common boilerplate. Some examples:

• <DefaultScene> would provide a default camera at some prescribed distance and size itself to fit into the browser window
• <OrbitCamera> would rotate/pan/zoom child objects based on mouse/touch actions, similar to the code already added by 8318719
• <Box> creates a box of a certain size and color
• <AutoMesh> handles the loading of mesh geometry and materials and things.

This will probably go into an addons directory or something similar.