[Doc] Create Documentation/. Move namespace docs.
[Doc] Update namespace doc for previous move.
Correct ProjectData include. Link ApplicationsLib.

Also update gui for moved ProjectData.
[Doc] Add Applications to doxgen inputs.
Remove unused GeoInfo and FEMEnums classes.
Remove remaining OGS/CMake and OgsLib occurences.
[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 empty GroundWaterflowFEM.
Merge remote-tracking branch 'origin/Boost156XmlWriterUpdate' into develop
Merge remote-tracking branch 'origin/MoveNamespaceDocumentation' into develop
Merge remote-tracking branch 'origin/SkeletonProjectData' into develop