Add rudimentary Travis CI hook

Travis CI (https://travis-ci.org/) is a fairly popular github based CI server, this adds support for the on_success and on_failure webhooks.

It requires the user enter their travis token, though as far as I can tell this is only used by github to trigger a new build and for the authorisation header of outgoing webhooks, so taking this information shouldn't be an issue.

Some extra configuration options might be nice, though.