Merge pull request #5 from opengm/master

from opengm master to my fork
first candidate for a fix of gurobi bugs...
This is untested since i do not have a licence of gurobi
on my home machine.
undid last commit ,was stupid
fixed gurobi bug
work in progress
fixed bug in constructor
fixed bug in constructor
refactoring
refactoring
gurobi refactoring
Merge pull request #118 from DerThorsten/master

gurobi is working!