added functionality for replacing and compressing mesh element values
mesh value editing functionality is now available in the gui
added <algorithm>-header for using std::sort method
Updated export submodules.
Fixing bug in merging geometries functionality.

Removing unused objects.
Removing the AABB object in destructor.
Fixing a memory leak in OGS4 geometries reader.
split up MshEditor class
Renamed method isPntInBV() and private attribute.

Renamed
- from isPntInBV() to isPntInBoundingVolume() and
- from _bv to _bounding_volume
to make the code more readable.
Merge pull request #117 from TomFischer/GeometryRelatedBugFixes

Geometry related bug fixes
Merge pull request #115 from rinkk/MaterialGroupModding

Material group modding