[ordering]
factor out that part of LeafGridView ordering which is independent from a gridview,
this is the first step for other functionspaces in the future, e.g. tracespaces
[test]
testnonoverlapping requires UG, so make sure we have UG available
[gridexamples]
fix out-of-source build

pass GRIDSDIR in the CXXFLAGS from the Makefile
[ordering]
improve documentation
[assembler]
directly derive GlobalDOFIndex type, don't rely on the Ordering, which should never know about a GlobalDOFIndex

The Ordering is supposed to change the natural ordering of the local DOFs,
thus it has nothing to do with the GlobalDOFIndex, which is actually a GlobalDOFId.
This patch is the first step to get rid of the GlobalDOFIndex typedefs and template
parameters in the ordering interface.
[ordering]
remove GlobalDOFIndex from the Ordering interface
[backend/istl]
adapt to the changes in the ordering interface

remove the, now, obsolete GDI template paramter