tests: test hook handlers in hooks-queue.py

queue: let's just call it event

queue: move option creation to main() to help with tests

viewer: move option creation to main() to help with tests

queue: turn HTTPErrors into JSON responses via BaseHookHandler.write_error()

queue: log event type that hook handlers receive

queue: handle invalid JSON payload by raising HTTPError(400)

queue: log payload as the original JSON string to ease testing

queue: handle ping event

queue: add preliminary GithubHookHandler