Merge branch 'integration_tests' into 'master'

Integration tests

Server-independent integration test case parser/player written in Python.
Currently the test is able to parse a subset of unbound test cases as described in:
- http://www.unbound.net/documentation/doxygen/replay_8h.html

The test cases are BSD licensed.

The Knot resolver mock context overrides the library calls to message sending functions,
redirecting them to the server with scripted answers.
The scenario can do following things:
- Simulate system time
- Provide scripted answers
- Send queries, compare responses

See merge request !4