[FEATURE] Add review webhooks

[thatkookooguy]

Change Summary

• assignees now populate the assignees attribute instead of the reviewers attribute on a pullRequest
• integrated 2 new github pull_request events [resolves integrate the new github code review system #29]
  • review_requested - adds a reviewer to the pullRequest data
  • review_request_removed - removes a reviewer and adds him to the history. history for removed reviewers is not unique. that's because the same reviewer can be removed multiple times
• integrated 3 new github pull_request_review_comment events [resolves integrate the new github code review system #29]
  • created - new review comment. add it to the reviewComments attribute.
  • deleted - deleted a review comment. removes it from the reviewComments attribute, and adds an history item inside history.reviewComments.deleted with the comment id
  • edited - changes the comment in reviewComments, and adds an history item inside history.reviewComments[<comment_id>] with the old message body
• integrated 1 new github pull_request_review events [resolves integrate the new github code review system #29]
  • submitted - reviewer submitted their review. this is populated in the reviews attribute. This holds all reviews by all users. reviews can't be changes, so every pull request review submits a new one and adds it to the array.

More info

right now, pull request review comments might appear twice! once in reviewComments and once in inlineComments. So achievements that want to check all comments should go to inlineComments and ignore reviewComments. reviewComments should be used for achievements that focus on code reviews.

tests will be implemented in a different PR

[coveralls]

Coverage decreased (-3.9%) to 39.885% when pulling 9f742ad on feature-add-review-webhooks into 2b5fa29 on master.

[coveralls]

Coverage decreased (-3.9%) to 39.885% when pulling bb369c0 on feature-add-review-webhooks into 2b5fa29 on master.

[thatkookooguy]

@ortichon I'll try and add tests on a different PR. I want to get this in so we can continue with other things