Websocket/HTTP abstraction

[diamondburned]

Since Lemmy is gradually moving from WS to HTTP, we should have a wrapper library that automatically detects if we can use its HTTP API.

Since we already have an API that effectively turns the WS into a request-response API, this should be trivial.

The following needs to be done:

• [x] Code generate Op-to-URL-route mappings
• [x] Abstract WS client behind an opaque API (request(op, data) -> response)
• [x] Make a HTTP client wrapper implementing that same API
• [x] Detect on profile creation if the HTTP API is successful, falling back to WS if not
• [x] Also having a client that can automatically fallback would be great.

[diamondburned]

Implemented!