Sync JIRA data to dashboard

This pull request adds automatic synchronization of JIRA information to the dashboard.  Most of the changes are in the back-end, where I've added tasks to fetch JIRA information (using the JIRA REST API), a cron job which consumes the JIRA RSS feed in order to keep the database up-to-date, and a model to persist JIRA information into the AppEngine datastore.

On the front-end, I've added two new columns, "Priority" and "Issue Type", which show information for the first JIRA issue linked to the PR.

Here's a screenshot showing how this looks:

![image](https://cloud.githubusercontent.com/assets/50748/5384924/87d2b882-8072-11e4-86e7-48d557eb141a.png)


Closes #37.