[PL] Add createDofMap() in Process.
[PL] Use number of node's DOF in createDOFMap().
[PL] GW: Add MeshSubsets and MeshComponentMap.
[PL] GW: Add _dof_map, calling createDofMap.
[PL] GW: Show future usage of the _dof_map.
Merge pull request #516 from endJunction/CreateDofMap

Create dof map