[FEATURE] Maintenance modes

[DaRacci]

The ability to define maintenance modes so you can allow different groups so you can define groups of players who can access the server with permissions like maintenance.<servername>.<group> or maintenance.global.<group>.

[FaultyFunctions]

To add on to this, it would be great if each mode had a separate MOTD, icon, etc...

I would like to define a mode for general maintenance and another one for when our resource world resets.