Add tests for pybal.util.ConfigDict

* Where available, use setuptools rather than the now-deprecated distribute.
* Declare a test suite under tests/.
* Add a tox.ini for better integration with Jenkins.
* Add tests for pybal.util.ConfigDict().
* ...more tests to come.

Run tests with 'python setup.py test' or using 'tox'.

Change-Id: Icbf989117b9c5b3aabfdca074675dbb8ed01cd45