1.) Segment functionality of the HeightFieldMesh has been moved to a new class HeightFieldSegment. Vector of these segments can be accessed by HeightFieldMesh.
2.) Texture size is now part of GlobalProperties (allowed values: 2^n, where n lies in [1, 10]). Default value is 1024.
3.) Each mesh based on HeightField (Zabaged grid, perlin, random faults, midpoint displacement, raster image) can use segments of a different size. Minimum (and also default) segment size is 32.
4.) User is now provided with progress (useful in case of texture download).
5.) Performance improvements. Invalid segments are now being discarded and their textures are not downloaded. This results in faster loading times and lower memory usage. In case of zabaged grid (segment size = 32), 204 textures are now downloaded (instead of 238).
