mod_http_oauth2: Add Cache-Control and Pragma headers per by RFC 6749 These are mostly for the various Client-facing endpoints, so the chance of browsers being involved is slightly lower than with the User-facing authorization endpoint, which already sent the Cache-Control header. Thanks to OAuch for pointing out.

This module produces more detailed HTTP logs for Prosodys built-in HTTP
server. The format is similar to that of Apache and go into Prosodys
normal logs at the `info` level.