Positive Z-levels(WIP)

Since I want to add a second floor to the Rivtech facility, I need to get positive Z-levels working, since a lot of the base is already there.

After diving into the code(including that huge if statement in mapgen.cpp), I *think*, I know what needs to be done to get it working.
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into positive-z-levels
Added sky terrain, sky overmap
Finished up, everything seems to work, as I want.
Added 3-D version of Motel
Added 3-D version of Office Tower(empty) thanks to acidia
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into positive-z-levels
Changed t_sky to t_open_air and changed the colours on them to make them more managable.
Fixed automap issue-apparently know up and know down are bad...
Transfered 3-D Buildings and made a mod.  Players will not be able to access new z-levels unless they use the debugger.
Reverted buildings back to their orignal settings.
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA into positive-z-levels
Fixed lab and military bunker mapgen errors
Fixed motel issue, by added a second version of the motel building.
added 2fmotel.json file
Merge remote-tracking branch 'dda/pr/7974' into dda-master

* dda/pr/7974:
  added 2fmotel.json file
  Fixed motel issue, by added a second version of the motel building.
  Fixed lab and military bunker mapgen errors
  Reverted buildings back to their orignal settings.
  Transfered 3-D Buildings and made a mod.  Players will not be able to access new z-levels unless they use the debugger.
  Fixed automap issue-apparently know up and know down are bad...
  Changed t_sky to t_open_air and changed the colours on them to make them more managable.
  Added 3-D version of Motel Added 3-D version of Office Tower(empty) thanks to acidia
  Finished up, everything seems to work, as I want.
  Added sky terrain, sky overmap
  Positive Z-levels(WIP)
Fix whitespace damage (mostly tabs).
Move t_open_air to end of list to avoid messing up legacy terrain loading.
Don't spam the player with messages about trivially visible traps.
Removed redundant overmap terrain definitions from z-level mod.