Split up test runs

For some inexplicable reason, the webhooks tests were consistently failing
when run as part of the whole testsuite, but passing fine when running only
tests/webhooks_tests.py on their own. Although ugly, by splitting these up
and calling each file with tests in it's own nose.run(), we can work around
this issue and have working tests again.
Merge pull request #180 from zoni/issue/175

Split up test runs