Bug 1020348 - Added a tab to show aggregations on the signature report page.

@peterbe r? It's a follow-up to https://github.com/mozilla/socorro/pull/2144
This is to hide the currently shown panel, then show only the one we are interested in when a user switches from a tab to another. The reason why I changed to ``#mainbody > .panel`` is because we have panels inside panels, and I don't want to hide the lower level panels.