[Dune] Default constructor in MultiLinearGeometry

[Oliver Sander]

Hi Martin,
last night I tried to switch from BasicGeometry to MultiLinearGeometry
for various parts of UGGrid.  Unfortunately, that didn't work as easily
as I hoped, because UGGrid expects a default constructor, which
BasicGeometry has, and MultiLinearGeometry hasn't.  Is there any chance
to get a default constructor in MLG, or should a adjust the UGGrid code?
best,
Oliver