FileIO -> MeshLib::IO.

In order to make OGS more modular:
- The {read/write}Mesh{From/To}File.{h,cpp} are moved from FileIO to MeshLib/IO.
- The FileIO/Legacy folder was moved to MeshLib/IO/Legacy.
- Include paths are changed according the changes above.

Move parts from FileIO to GeoLib/IO and BaseLib/IO.

Clears a warning from the compiler about missing prototope.

The GroundwaterFlowProcess is taken out because it does not exists for now.
This is an example.

- moved ProjectData.* to Applications/ApplicationsLib
- removed Vrpn folder in DataExplorer

This removes ProjectData ctor;

Also clarify an error message and the TODO for meshes.