[PL] Add number of node variables.

Element variables are not yet used.
[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.
Adjusted GUI for removed FEMCondition classes
[PL] Include class Process into ProjectData.
[Tests] Removed TestBoostXmlCndInterface.

The test tested class BoostXmlCndInterface, that is removed previously.
[CLI] Vector for storing ProcessVariables.
[ProjectData] Make attribute name readable/consistent.
[ProjectData] Add configuration of project to ProjectData.
[ProjectData] Path argument for ProjectData constructor.
[ProjectData] Functionality to read geometry.
[ProjectData] Functionality to read mesh.