Remove __pycache__.

Add CMAKE_MACOSX_RPATH=TRUE.

experiment with extracting required meta data for generating setup.py from
- dune.module file
- pkg_resource
This version does not require an extra project.py file but does assume that
the python module for which setup.py is to be generated is installed. Also dune.common
must be available:
- dune.common.module.Description class is used to parse dune.module file
- pkg_resource is used to extract additional metadata information (as provided by
  python/setup.py.in) requiring the module to be installed. This data is
  'description' ('Summary'), 'url' ('home-page'), 'author', and the install_requires.
  At the moment this will fail e.g. for dune-localfunctions which has no python
  package. We could decide to add the required information to dune.module and use
  replacements in python/setup.py.in instead.

Parse meta data from dune.module and setup.py.in.

add a try except around trying to open python/setup.py.in