Added damage map. Minimap works but tanks are not shown
Position and direction of tanks is correctly displayed in minimap
Tank position (height) and normal is deduced from vertex height now.
(Former position/normal was deduced form heightmap directly). Now the
tank behaves much smooter.
To prevent irregularities, the vertex position is set on cpu instead
gpu. Beacuse the height(x, y) function is not fast enough to calculate
terrain height in realtime, the vertices are cached in Terrain class.