mod_vcard_muc: take roles into account for access check
This allows admins on the MUC component to force-set avatars, even
if they are not owners in a particular MUC, similar to how they
are granted auto-ownership in other contexts.
Prosody 0.12 added an API allowing modules to report their status. This
module allows reading these statuses via HTTP for use in monitoring.
```
$ curl http://prosody.localhost:5280/status
{
"example.com" : {
"c2s" : {
"message" : "Loaded",
"type" : "core"
}
}
}
```