Port to PyQt5

All tests are passing locally; this won't pass on Travis since there is not python3-pyqt5 package on Ubuntu 12.04.
Try to build Qt5 and PyQt5 on Travis CI
Fix typo
Reduce verbosity
(Re) add support for multiple Qt frontend:

 - PySide: tested on travis
 - PyQt4: tested on travis
 - PyQt5: not tested on travis
Fix pyside install
QTest support is incomplete for PySide

This means we do not test the PySide frontend
Travis: fix allowed failures
Update compile ui to replace PyQt5 by pyqode.qt
travis.yml: fix syntax error
Fix a few bugs
Do not cover the qt package (at least for now)
Fix PEP8 errors
Travis: run PEP8 tests only in PEP8 env
Fix a few more bugs with pyside
Finish feature/pyqt5

Fix #40 PyQt5 is now supported !

#113 We keep PyQt4 and PySide support

At the moment, only PyQt4 is tested on Travis. PyQt5 support has been tested locally. (on an archlinux box), PySide support cannot be tested due to a lack of methods in QTest (qWait,...)

I have no interest in PySide but I will accept contributions that improves the situation: if you care about pyside support, submit a PR that adds the missing methods to QTest and enable testing on travis.