Requirements update

Bumped the version of MySQL-python from 1.2.4 to 1.2.5 due to the
following issue:
http://stackoverflow.com/questions/21198881/error-when-trying-to-install-django-cms-in-virtualenv-w-mysql-on-mac-osx

As invtool is not published on PyPI (at least I couldn't find it), I've updated the requirement to
pull it directly from GitHub.