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
My rationale was to say that we don't want such debugs in production mode, and we still can add console.log where we need when in debug mode.
For sure another option would be to make those debugs active only when in DEBUG=True, but AFAIK there isn't any bridge that make this available in JavaScript.
We are a bit a in a "clean mode" those days, so please forgive me if you think I've been too far on this one :)
What would be your preference here?