Implement server notices (usermode +s)

This implements the server notice mechanism. It adds umode +s which acts as a listmode and keeps track of what users are subscribed to what events. It supports using multiple mode parameters using commas and can list what events the user is subscribed to. Oper permissions are split into different permissions for each event with a "servernotice-all" wildcard permission. It also implements the following snomasks:
- connect
- quit
- remoteconnect
- remotequit
If you're going to base the `subscribeLists` on `mask`, you may as well do it here, too--it'll avoid issues when someone is ridiculous and sets the same snomask multiple times with different case and only unsets some of them (where it's still set and they should still get notifications, but they won't).
If you standardize the case here, 1. the modes will only be set with the correct case, and 2. the mode handler will handle duplicates for you.