Add unit test for MajorChangeListener.
Rename MajorChangeHandler#run to #start

Fits better with #stop.
Extract MajorChangeHandler.
Fix typo.
"group" not "groups" in Bundler, even inline.
Rename executable to use underscores.
Use a provided logger instead of STDOUT.
Add integration tests.
Merge pull request #2 from alphagov/add-tests

Add tests