Make log rotation configurable et. al.

This patch series essentially makes log rotation configurable. This was required because we wish to have log rotation handled by logrotate and not python. Especially, because we use multiple WSGI workers and they can get confused when they all try to rotate their logs at the same time. 

In order to support this feature in a clean way, we had to refactor the ``logger.py`` file. We should also mention that we have covered this with unit-tests to make sure the code is at least sane and free of syntax errors and such. During the testing, we discovered that we had to test for different versions of python and provide a backport for python 2.6. Thus, testing with ``tox`` has been set up to test python versions 2.6 and 2.7.