Merge pull request #1 from espressomd/master

Updated fork
Constraint "plane" is no obsolete. Tunable slip feature can now be used
with the constraint "wall".
Added ifdef for tunable_slip feature for "wall" constraint.
Merged 'espressomd/master'
Now constraint plane cell is deactivated
Merge pull request #194 from KaiSzuttor/master

Added ifdef for tunable_slip feature for "wall" constraint.