BaseGenerator adds the hability to backup some data on which nodes
and edges are created. However when creating a second graph with the
same generator, this data must be cleaned up. This has been added
in a default "end()" method. Each generator has been modified to
call this super.end() method.

The algorithm is now largely tested in weighted and unweighted
graphs and should work on non-multi-graphs. It works on directed
graphs, but ignore the direction.

Added the possibility to register a progress "callback" since
the algorithm can take a lot of time to compute.

Also removed the extraneous @override in Community.

Merge branch 'feature/community-measures' of http://github.com/gjherbiet/gs-algo into gjherbiet-feature/community-measures

Merge branch 'feature/community' of http://github.com/gjherbiet/gs-algo into gjherbiet-feature/community

Community algorithms don't manage GUI display properties any more, only place nodes on a specific class, related to their current assignment.

Decentralized community algorithm now use same attribute name uniqueness method as other algorithm (e.g. Dijkstra).

DecentralizedCommunityAlgorithm now accepts a Random object instead of a seed for controlled random number generation.

Merge branch 'feature/community' of http://github.com/gjherbiet/gs-algo into gjherbiet-feature/community

Merge branch 'feature/community-measures' of http://github.com/gjherbiet/gs-algo into gjherbiet-feature/community-measures

* master:
  a0dffa4e