[A] Remove unnecessary virtual function specifier.
[A] Document ProjectData class.
[A] Correct ProjectData function names. Correct constness.
[A] Add mesh check in ProjectData::parseProcessVariables.

Also clarify an error message and the TODO for meshes.
[A] Move unused (from outside) methods into private sec.
[A] Use non-static member init for ProjectData::geoObjects.

This removes ProjectData ctor;