Rename 'tileset' global variable to 'tilesetDir' for increased readability.
qtscript: Add 'tilesetType' constant that says which type of tileset the map uses.
It is one of "CUSTOM", "ARIZONA", "ROCKIES" or "URBAN".
Add generic VBO drawing class called GFX (for lack of better name).
Port all VBO drawing other than PIE model and terrain to GFX class. This
also fixes GPU memory leak bug when changing skybox, hence closing ticket:3842.
Port radar texture display to GFX class.