Checks for a parameter named subdomain and if it exists, adds it to the roomname as used in multiple domain mode ([subdomain]roomname@conference.example.com).
Moves muc_size module to per-host module and adds token verification.

Adds and the default conference. part where the muc module live in default deployments.

This reverts commit e2e04e3f16.

Queries room for their size or room particiapnt's information. Depends on luarocks net-url module.