.obj export / import needs improvement

This export / import function is very basic. Some aspects that need to be changed:

Check that import of normal vectors all showing up works (refer to example from M.) - DONE
swap z/y coordinates as in blender
Check that really right scaling to meters is achieved (refer to comments of M.)
allow import / export of different terrain types; especially important for terrainWater - DONE for Water
Allow exact rectangle extraction to directly map an ortho photo on corners of extracted mesh - IMPORT at outer border possible
Show error when CENTER COORDINATES have been moved and thus import is outside area

nofaceinbook / muxp