mod_http_oauth2: Namespace the various codes to minimize confusion Both for the programmer and in OAuth flows. While unlikely, it should not be possible to cause weirdness e.g. by typing a client id and authorization code into the device code entry.

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.