Refactor `generic` and `facades` modules with better names

[Mourits de Beer]

We want to standardise naming/organisation convention such that all route definitions are defined in a module routes, with custom model definitions in models; utility methods moved to utils; etc.

This can be followed up with another PR to simplify any methods that are too complicated. Ideally, route logic should only define routes - any complex logic should be moved into its own module. It seems like this was the intent of facades, but I think that's a very unclear name. I suggest services, which can then contain a .py module for the route logic.

In summary:

• generic -> routes (stripping code to only contain route logic)
• facades -> services (moving all route logic to appropriate modules here)
• custom models, exceptions, and helper methods, should be moved to models, exceptions, and util, respectively.