MultiServer: Support location name groups in !missing and !checked commands

[NewSoupVi]

If the second argument of "!missing" or "!checked" is a valid location group, return all missing/checked locations from that group.

This also means adding @mark_raw to _cmd_missing and _cmd_checked, as there are location groups with spaces in them.

Tested:
Tried it with the new location groups in Witness, don't know what else to test

[NewSoupVi]

To be clear about my personal motivation:

The Witness is introducing "area hints" to audio logs, such as

In the Quarry area, you will find 4 progression items.
2 of them are for other players.

I also added these areas as location groups.

It'd be nice if the player had an easy way to look up all the locations that exist in an area that they just got a hint for so they can use these hints strategically.

I can obviously try to figure out an in-game/in-client UI for this, but I think this is also just a nice feature, that doesn't require a bunch of new stuff, that people will potentially appreciate regardless of game

[Ixrec]

Confirmed !checked and !missing now work with my location name groups, even ones with spaces.

Before:

After:

This is a world where I've already checked almost everything. I also tested on a fresh world with nothing checked, and got the (correctly) opposite results where !checked prints nothing and !missing prints everything.

Code also LGTM.

[Exempt-Medic]

Tested out the changes and tried numerous ways of "breaking" it which all failed. Code LGTM