Move HTTP API server out of librqbit

[The-Minecraft-Scientist]

Currently if I add librqbit to my project it pulls in a ton of massive dependencies (axum and co) required to run the web API. Ideally the crate on crates.io would contain the minimal number of dependencies required to download torrents via rust functions (i.e. using the Session API). I might make a PR that does this at some point soon.