* Refactored a few things in Scene to make maptile saving easier to understand.
* Added comments to describe the 'clever code' assetcache update without the gridasset being updated so as to lessen possible confusion in patches in the future.
* If the MapImageModule isn't loaded, default to the code in Scene still.
* Fixed a bug with Terragen loader where it would do bad things on a non 256x256 sized terrain. Now loads the array correctly.
* Moved MapImageModule.cs to Modules/World/WorldMap
* Changed Location.RegionHandle to use Helpers.GetUlong instead of doing it ourselves.