HeightMap class: change Point types to TilePos

[AaronVanGeffen]

The HeightMap class (HeightMap.h/cpp) currently uses a custom Point struct for its coordinates. I think we should move to use the usual TilePos vector type instead.

[ShuraxN]

Hey, I would like to work on this issue, but I am not sure what a TilePos vector is and would like if it is defined in the tile.h file.

[AaronVanGeffen]

Thanks for your interest in working on this. The TilePos2 vector type is defined in the World.hpp header.