Add back cobalt support

[Fleeym]

Cobalt support will be very "DIY", to prevent misuse of any specific cobalt instance.

Users will have to either find a suitable cobalt instance that works for their use, or self-host (easiest way to actually gain back YouTube downloads).

Besides YouTube, we're getting some other platforms cobalt supports, notably soundcloud, which should be useful.

Checklist

• Get metadata fetching properly working
• Try to get information about the cobalt instance when setting it up (supported services, etc)
• Implement the actual song download
• Possibly refactor Nong.hpp yet again since it's terrible at the moment