Add hook inside drupalchat_verify_access

We have had multiple requests for users and groups to be able to completely disable chat for themselves or their og groups due to various issues - particularly folks who are inside a network that firewalls off drupalchat for whatever reason, resulting in an unusable website (we can't go async due to login/logout issues IIRC).

While this entire request *could* be fulfilled inside the drupalchat module, perhaps it would be better to ask for a hook so I can implement it in our own module.

If we could add a hook inside drupalchat_verify_access for other modules to be able to disable chat, that would be very handy. Something like this:

$verify = TRUE;
  $verifies = module_invoke_all('drupalchat_access');
  if (is_array($verifies)){
    foreach ($verifies as $response){
      if($response === FALSE){
        $verify = FALSE;
      }
    }
  }

right before the return, and then add
&& $verify
into the end of the return line...