Make unit tests pass

Just some minor fixes to make the unit tests pass.

I've essentially just loaded Hubzilla (via boot.php) before the tests run. This ensures that global constants and other stuff needed by some of the code under test is available during the tests. Not exactly unit test clean from a purist point of view, but a pragmatic approach that allows addin tests adn increasing test coverage before breaking stuff 😄

Also corrected a minor error in the Markdown test, as the Markdown lib now seems to correctly convert the less-than entity as well.

Other than that I have not done anything with the tests themselves. Just trying to get everything to run and to figure out how everything is coupled for now.