sixtracklib: Update default settings file Settings.cmake.default
sixtracklib: Update default settings file Settings.cmake.default

- Regroup setting sections to improve visibility for commonly used
  options

- Add additional settings concerning handling of examples, unit-tests,
  and testdata during the install step (i.e. make install)

  TODO: Finish implementing this, cf. also
  https://github.com/martinschwinzerl/sixtracklib/issues/5

- Add options for enabling/disabling the generation of C++ and Pyhton
  bindings. The selective disabling of C++ bindings is currently prepared,
  the Python support has not been properly started. This is in anticipation
  of proper Pyhton support.

  TODO: Implement handling according to these settings

SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib