Feature/proximal newton solver

Introduce a Riemannian Proximal-Newton Solver as an alternative for the Trust-Region Solver. Also add 3 cleanup commits.

src/film-on-substrate.cc

@@ -217,11 +217,11 @@ int main (int argc, char *argv[]) try
 
     grid->adapt();
 
-    grid->loadBalance();
-
     numLevels--;
   }
 
+  grid->loadBalance();
+
   if (mpiHelper.rank()==0)
     std::cout << "There are " << grid->leafGridView().comm().size() << " processes" << std::endl;