Plumb /organizations/{org_id} into HTTP API

Adds /organizations/{org_id} routing to the REST API.

Also includes a refactoring/simplification of the test_resources.py
tests, using a patcher method on the base test case class to avoid
repetitive calls to mock.patcher.start and addCleanup.
Merge pull request #22 from jaypipes/groups

Plumb /organizations/{org_id} into HTTP API