Remove custom WebSocket code (#4001)

* Remove custom WebSocket code

Remove our custom WebSocket code and only use the Rocket code.
Removed all options in regards to WebSockets
Added a new option `WEBSOCKET_DISABLED` which defaults too `false`.
This can be used to disable WebSockets if you really do not want to use it.

* Addressed remarks given and some updates

- Addressed comments given during review
- Updated crates, including Rocket to the latest merged v0.5 changes
- Removed an extra header which should not be sent for websocket connections

* Updated suggestions and crates

- Addressed the suggestions
- Updated Rocket to latest rc4
  Also made the needed code changes
- Updated all other crates
  Pinned `openssl` and `openssl-sys`

---------

Co-authored-by: Daniel García <dani-garcia@users.noreply.github.com>