Add support for per-tile minimap color and height/ramp type.
TileSet cleanups.
Rename TileTemplate -> TerrainTemplateInfo.
Load tmp(ts) ExtraData for cliffs etc.
Work around the undesired R8 terrain sprite offsets.
Convert TS terrain height, ramp, and minimap colors.
Introduce TerrainTemplatePreviewWidget.
Merge pull request #6855 from pchote/heightmaps-part-one

Add groundwork for heightmapped terrain.