DMlibMesh

This removes the need for PetscDMNonlinearSolver when using DMlibMesh.
In particular, this removes the need for PetscDMNonlinearSolver when solving VIs.
miscellaneous_ex7 has been updated to reflect that as well as the changing PETSc names for VI solvers.
The present treatment of DMlibMesh also makes it easier to extend this DM, 
DMMOOSE of www.mooseframework.org can, for example, move much of its generic
DMCrateXXXDecomposition() functionality into DMlibMesh and only extend the pieces 
necessary for the support of MOOSE-specific contact-based splits.
Similarly, the geometric multigrid support, when added to DMlibMesh, will be usable
from derived DMs.