Automatically add default filter subscription when necessary. Several other changes along the way:

* Pass in application locale to the JS engine
* Allow passing arbitrary parameters in _triggerEvent()
* Add FilterEngine::IsFirstRun()
* Make Utils.checkLocalePrefixMatch() and Utils.chooseFilterSubscription() more like what they are in Firefox

--HG--
extra : rebase_source : 84ee7d9ddd7e00c4fd176b8c8bdcab3555469cc7