Bug 967994 - Implement various levels of rocketness

https://bugzilla.mozilla.org/show_bug.cgi?id=967994

This implements three levels of configuration for the ROCKETBAR build flag.

none - No rocketbar, everything should be the same as 1.3.
full - Full rocketbar experience, browser app is removed.
half - Rocketbar is present along with the old browser app. Tapping on links will show an activity with two options, one for the Browser, and one for the System.