Rewrite: Initial structure

[JJTech0130]

Trying to get the ball rolling here, this is my proposal for an initial structure of the rewrite.

I've structured it so that APNs will eventually be published as it's own independent PyPI package. The first stage of pypush's rewrite will be to rip everything out, and polish off just APNs by itself.

Still need:

• [ ] Rewrite actual APNs implementation, using asyncio this time
• [ ] Work out API for device details and versions