Repair Flowdock adapter for ChatBot

Summary:
Restores functionality for Flowdock->Chatbot adapter.

Most likely the result of API changes in the year since the original patch was contributed,
the flowdock adapter no longer worked.

This makes a few tweaks to both the base streaming adapter class and the flowdock adpater. I took care to not disturb the functionality of the campfire adapter, but I don't have any way to test it.

Test Plan: I am new here and I have no idea what to write other than sarcastic things but I'll most like amend this after review.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10168