Assimp importer was switching x-axis to a -x-axis... not acceptable...
because the data i exported used the axis the other way around.
Now the custom exporter export all the data, so mesh and collision data as
well as difficulty, type and rotation which (atm) need to be inserted
manually.

Importer uses rapid-xml

When modeling a start point for the segment can be set. The positive
y-axis(in Blender) defines the forward direction for the TunnelSegment.