Bug 1100295 - Implement navigation logic. r=crdlc

Yep, all panels by default are hidden [1], just the one with the 'main' class is the one shown.


[1] https://github.com/mozilla-b2g/firefoxos-loop-client/pull/310/files#diff-f1f9584076d234531bd31a0e1a18a347R14