Support merging user configuration and system configuration.

mutalyzer/config.py:
- Try to load system configuration and user configuration, in that order, and
  merge them if we find both.

tests/test_website.py:
- Use running webserver to retrieve batch results.

extras/config.user.example:
- Example user configuration, overwriting some values from system
  configuration.


git-svn-id: https://humgenprojects.lumc.nl/svn/mutalyzer/branches/refactor-mutalyzer-branch@336 eb6bd6ab-9ccd-42b9-aceb-e2899b4a52f1