Adds the ability to query or set whether the game is in Map View.


Rationale: Though not necessary, it's analogous to allowing the script to set the WARP mode.

Syntax:
```
  // Querying:
  if MAPVIEW { print "I am on map view". } else { print "I am in flight view". }.

  // Setting:
  set MAPVIEW to true.
  print "Now looking at the map".
  wait 5.
  set MAPVIEW to false.
  print "Now looking at flight view".
```