Setup issue webhook to handle issue notifications from the various repos

[acorncom]

This issue is part of our #7 MVP roll-up issue.

I believe we'll want to have an active web hook listening for this payload:
https://developer.github.com/v3/activity/events/types/#issuesevent

Based on that information, we would need to confirm that we're actively tracking this repository and then update the appropriate issue tags in Firebase.

We'll want to handle the following cases:

• closed
• reopened
• labelled
• unlabeled

I have setup a repo here: https://github.com/acorncom/ember-hitlist-tester to help with handling web hook notifications. If someone would like to be a contributor on it so they can add / remove labels, just let me know ;-)

[acorncom]

Closing in favor of ember-learn/ember-help-wanted-webhook#1