Move components to correct hexagonal layers

[kirypto]

• [ ] Move RestHandlers to the application layer. They must not contain flask logic or flask dependencies.
• [ ] Move the definitions of the routes to the RestHandlers. One way of achieving this would be having the <Entity>RequestHandler methods return a Tuple[str, Callable] or similar so that the RestHandler can return the route as well as the method for accessing it.
• [ ] The abstract <Entity>RequestHandler can likely be combined back into the Rest<Entity>RequestHandler, as it is not needed with the latter in the application layer.

[kirypto]

To add to this, if the Rest<Entity>RequestHandler classes could return a Set[Tuple[<route>, <http method>, <handler function>]]. This way the flask controllers could be simplified to iterating across the set and setup corresponding handlers. A little extra may be necessary to tie in whether or not the json should be extracted and passed through.