mod_http_oauth2: Allow user to decide which requested scopes to grant These should at the very least be shown to the user, so they can decide whether to grant them. Considered whether to filter the requested scopes down to actually understood scopes that would be granted, but decided that this was a bit complex for a first step, since role role selection and other kinds of scopes are mixed into the same field here.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.