robot.paths attribute is now handled as a dictionary
GLPK solver for TOP formulation

TOP = Team Orienteering Problem

Use pymprog and its bindings to the glpk solver.
The formulation is slightly different (easier and lighter actually) than
the *.mod files, due to available data and python features.
FIXME: robot position should be given as pixels
Reduce the number of sampled points to ease glpk tests
Fix MTZ constraints
GLPK solver update robots' plans
Plans are now displayed too
Update starting positions
Clean up robot positions
Display is enhanced and shows starting positions