varregion: push TerrainData implementation up and down the database storage stack.
Implement both LoadTerrain and StoreTerrain for all DBs.
Move all database blob serialization/deserialization into TerrainData.
varregion: enforce multiple of 256 for region size when parameters fetched from user.
Output info and warning messages for non-legacy region sizes.
varregion: fix lawn-mower terrain fill so it works for non-square regions.
Add some debugging logs on region creation to report region size.