Generate url infrastructure for hosting services so that they can be called to access web hooks. Added repo_urlpatterns to the service base class. Modified registration and unregistration of hosting services to add and remove urlpatterns respectively.

Wrote test case HostingServiceUrlPatternTests in hostingsvcs.tests.py. I've tested the addition and deletion of url patterns during registration and unregistration, respectively. Added tests for cases when the url_patterns are not defined. Also tested adding bitbucket url patterns (see screenshot). All tests have passed. :)