Targets:
* Runs the unit-tests for python 2.7
* Tests unit-test coverage
* Try to build docs
* Code style checks:
* flake8
* isort
Codes changes:
* Fixed tests for httpdownloader (using tmp dir)
* Implemented a couple of tests for Stats plugin but they fail to run on travis
Issues:
* Can't get py26 to work because of installing libtorrent through apt and
the option system_site_packages fails for 2.6.
