Issue #87, Step 1: Break Hipchat actor into multiple classes.

Move common methods into a HipchatBase actor class, split up unit tests
as well.
Issue #87, Step 2: Implement hipchat.Topic actor.

Full actor code, unit test and integration tests.
Issue #87, Docs
Issue #87: Quick indent fix
Merge pull request #131 from Nextdoor/issue_87

Issue 87 - Add hipchat.Topic actor