Display Dashboard notification if system is configured using meetme

With the announcement that Asterisk's meetme module is deprecated and scheduled for removal in asterisk 21, we should display a dashboard notification if the system is confiugred with meetme.

This would only affect a small number of users, those that have upgraded continuously from old fbpx versions where meetme was set as default, or who have restored from very old backups. I don't believe there is a single feature provided by meetme in FreePBX that can't be done with confbridge. The change should be invisible to users and admins.

The Conference Room App paramter in Settings -> Advanced Settings is currently set to app_meetme. As this Asterisk module is deprecated and scheduled for removal in Asterisk 21, it's recommended that it be changed to app_confbridge.