Implement "patchr" as a d.o user enhancement

Problem/Motivation

The most compelling reason to use dreditor is it's patch review feature. Core mentoring has being including it in their workshops for a few years and it seems worth while to include it in drupal.org.

Proposed resolution

Port dreditor's patch review system to drupal.org.

Remaining tasks

1. Implement it
2. Deploy

User interface changes

API changes

Data model changes

Background

• https://groups.drupal.org/node/313158 has some discussion about interface for reviewing