fixes bug 758054 - reportslist should only populate tabs when clicked

@ossreleasefeed @rhelmer r?

First of all, I know this is a massive patch and I'm sorry about that. 

The major difference here is that ALL tabs on the reportlist page now load lazily. The view `report_list()` does NOTHING with any data so clicking on a signature now will load super quick which is nice. 

The most important "bad" thing about this new approach is that we can no longer decide to include or not include the "Bugzilla" tab. It used to depend on there being bugs. 
The other thing is that it used to load the "Comments" tab with a number. E.e. "Comments (7)" but it can no longer do that because you don't know how many comments there are in the database until you've clicked it. 

To review this, the most important thing to do is to pull it down and test it locally with your data and/or fakedata. 

I'll try to add some comments to my own code to help the review.