Regression testing of dependencies

[i-keliukh]

We need to implement extended testing for compatibility with various OS versions and dependencies versions. The test should install test environment on several versions of supported OSes and install several versions of dependencies in different combinations. Then, on each variant a full test suite has to be performed. The detection of dependencies and installation of versions has to be automatic, based on setup.py. Since this test would take much time, it should be done once a week against committed sources only. As an option, a badge can be displayed on a main page of the repository.

Relates to #280.