[Cleanup] Rename: DIM -> MY_DIM for UG

src/Makefile.am

src/assemblers_tmpl.cc

src/boundary_writer_tmpl.cc

src/coupledtimestepper_tmpl.cc

src/explicitgrid.hh

src/explicitvectors.hh

src/fixedpointiterator_tmpl.cc

src/friction_writer_tmpl.cc

src/sand-wedge-data/mygeometry.hh

src/sand-wedge-data/mygrid.cc

src/sand-wedge-data/mygrid.hh

src/sand-wedge-data/mygrid_tmpl.cc

src/sand-wedge-data/patchfunction.hh

src/sand-wedge-data/twopiece.hh

src/sand-wedge.cc

src/solverfactory_tmpl.cc

src/timestepping_tmpl.cc

src/vtk_tmpl.cc