Added issue tracking integration for drafts and review requests.

Features:
- shows all issues that have been dropped/marked as fixed since the latest revision (if one exists)
- updates as issues are reopened/dropped/marked as fixed
- it also appears in the DiffViewer (however, the anchors do not work, but I'm not sure what I should do to fix that)

Problems:
- I changed some of the Issue Summary code, most notably in reviews.js, views.py and review_detail.html. (either for clarification, or to be able to reuse elements in my code)
- Currently, the computation is somewhat duplicated in 2 areas (this is partially because I wanted to remove the need to iterate over the comments multiple times). If this isn't a big issue, I can remove the summarization from the View and the need for a hash filter.
- I have a couple changes here that are reflected in http://reviews.reviewboard.org/r/2858/

Local dev testing was done on Linux (kernel 3.2.4) with Chromium 17.0.963.46.

Additionally, I was able to successfully receive an e-mail with the desired information.