fixes bug 907855 - cache bugzilla summaries for fasster Top Crasher

@rhelmer

Also perhaps @ossreleasefeed wants to take a look. 

The idea is that when the `buginfo()` does a lookup, it caches each bug's metadata. 
Then, when you render the topcrasher or search results or report index, if there is something in the cache for a particular bug that gets inserted into the template to look like this:
```html
<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=897503" 
 title="Find more information in Bugzilla" 
 data-id="897503" 
 data-summary="crash in nsHttpConnectionMgr::OnMsgShutdown mainly with Leethax.net extension" 
 data-resolution="FIXED" 
 data-status="VERIFIED" 
 class="bug-link bug-link-with-data">897503</a>
```

Then in bugzilla.js what it does is loop over all `a.bug-link-with-data` elements and sets up the relevant title and stuff. 
Then, if there are any links on the page that don't have data. I.e. that look like this:
```html
<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=897503" 
 title="Find more information in Bugzilla" 
 data-id="897503" 
 class="bug-link bug-link-without-data">897503</a>
```
(note the different class names)
It then fetches all the data for these and sets it on its data attributes. Then, again the function is called that sets up the relevant title and stuff. 

A very important change here is that:

* How bugzilla link's appear is **cached for 1 hour**
* Rendering Top Crasher (for example), when caching warms up is going to be much faster since much less XHR is needed