Test on python 3.3 and 3.4 with travis

Created by: nikolas

Python 3.2.x is deprecated, so I thought it would be good to get tests running on some newer pythons. I've switched from the python3-gi package to using 'pgi' from pypi, because the apt-installed python3-gi was having trouble importing.

pgi requires python 3.3+ (see: https://pypi.python.org/pypi/pgi), so I've removed python 3.2 from the test matrix. Let me know if we're using python 3.2 anywhere, but as far as I know plinth is run on python 3.4.3 with debian sid on the freedombox image.