Refactored API code into subpackage

[ErikBjare]

The idea is to split the big resources.py file into smaller files, like the code examples for flask-restplus.

[johan-bjareholt]

Why are you working on refactoring aw-server-python when aw-server-rust has feature parity and will be replacing it?

[ErikBjare]

Because it is still the reference implementation, and faster to prototype stuff in.

[johan-bjareholt]

But it's just refactorization, it doesn't add any functionality? Why spend time on refactoring something that we don't intend to keep for a longer period of time?

[ErikBjare]

Because I wanted it to follow the coding conventions of the flask-restplus example projects, which will make it easier for me to follow the examples here (JWT) and here (OAuth2) as well as make me properly learn how to structure flask-restplus projects in general.