[BOGOSS-40] PrestonBot should be allow to request changes on Pull request - first part

[prestonBot]

This issue has been migrated from the Forge. Read the original ticket here.

• Reporter: mAndrieu
• Created at: Thu, 15 Sep 2016 16:53:57 +0200

Basically, since GitHub have introduced a Review system (https://help.github.com/articles/about-pull-request-reviews/), PrestonBot should request changes on Pull request template when its invalid.

This will enforce the quality of future changelogs, the quality of contribution and once it's done this need no more human efforts.

Of course, when the changes have been made, PrestonBot should approve the pull request.