Add Bugwarrior and its dependencies.

This pull requests has one commit for each package.

This include all dependencies which are needed to get bugwarrior working, including a few patch to fix the test suite of python-bugzilla, and a patch to make sure that we bake-in the dependency of taskwarrior in python-taskw (which is useful for running bugwarrior-pull in a service).

The test dependencies of bugwarrior are not all satisfied yet, but so far it is working fine for bugzilla & github on my computer.