[Bug 871243] Auto update smart folders' icons [r=crdlc]

https://bugzilla.mozilla.org/show_bug.cgi?id=871243

The shortcut icons that come bundled with the phone are never updated. When a user changes location and UI language so do the results he gets - therefore we need to trigger icon refreshing in these 2 cases. Also, at a given interval (because results change in the API).

We do this by having a Tasker.js object that waits for any of the 3 triggers to update the icons.