Bug 1020348 - Added new signature-based report with a simple data tab.

I think @peterbe, @lonnen or @rhelmer can review this. It's django only, no back-end changes. 

Note that this is a first version that I am sending now for the sake of smaller PRs. The page only shows a list of crash reports at the moment, but it should work fine. It is not linked from anywhere yet, and is hidden behind a waffle switch, so it's safe to release it as is. I'm working on adding two other tabs asap, one for aggregations and the other to list comments. 
perhaps this function is awesome but you should consider something like [this](http://jsfiddle.net/v92Pv/23/) instead which looks like it's been battle tested by lots of people.