Add Twitch, error handling, revokation changes, etc

Refreshable connections, refactoring, access-token endpoint ...

- Aded /users/@me/connections/:connection_name/:connection_id/access-token
- Replaced `access_token` property on ConnectedAccount with `token_data` object for refreshing tokens
- Made a common interface for connection things like ComonOAuthTokenResponse
- Added `RefreshableConnection` class
- Added token refresh to Spotify connection (disabled)

Switch from Github real name to username for GH connection

Add discriminator usernames for Discord connection

fix discord connection

Add spotify connection

Add reddit connection

Add facebook connection

add epic games connection

WIP Discord connection

`handleCallback` returns connection if created for `USER_CONNECTIONS_UPDATE`

adding connection now works

add connections