GitLab

- Switching from enum indexed to String indexed Attributes 
- Merging unassociated function into classes 
- Supporting const variants of most Graphtheory classes 
- Increased Support for error handling 
- Correction to Graph copy assign operator 
- Renaming Basic_Graph.* to just Graph.* and Graph.h to Graphtheory.h 
- Eliminating Graph Specializations as they are no longer necessary 
- Adapting Maintenance_Problem classes to support new Attribute system

- Now scans integrality under "General" und calculates the convex hull 
wrt these. Previously all variables were assumed integral.
- Adds calculation of projection on Integral Coordinates and subsequent 
convex hull.

(previously nodes may be visited multiple times)

fixing signs for polymake compatibility