[ML/Tests] Fix warnings in tests.
Merge pull request #499 from endJunction/FixWarningsInMeshLibTests

Fix warnings in MeshLib tests.
[PL] Add mesh subset to initialize().
[PL] Initialize MeshSubsets and MeshComponentMap.
[PL] Rename mesh_items_all_nodes; items->subset.
[PL] Add destructor for GroundwaterFlowProcess.
[PL] Move mesh_component_map to class variables.

...from the initialize().
Also delete it in the dtor.
[PL] Add createDofMap() in Process.
[PL] Use number of node's DOF in createDOFMap().
[PL] Remove MeshComponentMap include from GW.
[PL] Add dof_map to GroundwaterFlow.
[PL] Empty solve().
[PL] Add initialize debug message.
[PL] Add simple GWFprocess::post() writing result.
[PL] Add next steps for solve().
[PL] Add GlobalSetup as template to GW process.
[PL] Add global matrix and rhs/solution vectors.
Add LinearSolver to GWProcess.
GW: Make linear solver happy with identity matrix.