handling of python bindings by dune-project and dunecontrol

duneproject

• no support for adding python bindings to a new project.
• for the pip installation we have added some new (optional) fields to dune.module (see !900 (merged)) which would be nice to have in new modules as well.
• In the list of found dune modules it would be good to disregard a possibly found dune-py since no module should depend on that.
• A README file is generated but perhaps that should be README.md?

dunecontrol: fixed

• if dune-py is found dunecontrol tries to build it but fails (it's in source build). This module should be ignored by dunecontrol - possibly this needs to be done in dunemodules.lib