Site profile "community" should be invite-only by default

Because if you have your own local/closed community, likely you
don't want random newcomers that drop in, spam and leave dead
accounts.

The Admin can of course always override this by setting the config
"inviteonly" to false either in the config.php or on the website.

lib/siteprofile.php

@@ -191,6 +191,7 @@ class CommunitySite extends SiteProfileSettings
             'site' => array_merge(
                 $config['site'], array(
                     'private'    => false,
+                    'inviteonly' => true,
                     'closed'     => false
                 )
             ),