Allow choosing between old and new implementations.

* We can change between an old and a new implementation for the global
  stategraph.
* We can change between an old and a new implementation for instantiation and
  solving.
For both see cases/__init__.py

Also remove the -v flags from all tools.
Change experiments such that the only old tool that is used is pbes2bes.

Also update the mCRL2 versions that are installed and used by the shell scripts.
Merge branch 'master' of github.com:jkeiren/pbesstategraph-experiments