Refactor and update test to pass on gtk 3.8 using nosetests
Mark some code as not to be covered with tests
Derive all classes from object explicitely

This fixes annoying warnings like:
/usr/lib64/python2.7/site-packages/gi/types.py:226: RuntimeWarning: Mixin class dogtail.tree.Application is an old style class, please update this to derive from "object".
  RuntimeWarning
Run tests on travis and report to coveralls