Cast stats counts as integers (bug 997465)

Also:
- use a setting for the collector addon
- remove dbg from stats/manager.js

Ref: https://bugzilla.mozilla.org/show_bug.cgi?id=997465
It never gets out of [this](https://github.com/mozilla/olympia/blob/master/media/js/impala/stats/manager.js#L528) as a string, according to my tests.
If you know well this part, you may have indication to share [here](https://bugzilla.mozilla.org/show_bug.cgi?id=997465#c6), grazie :)