move My Submissions to primary nav (bug 860373)

Note that only comment #13 (https://bugzilla.mozilla.org/show_bug.cgi?id=860373#c13) is relevant. The discussion around this minor issue got a bit out of hand and was reined back in.
Re-purposing wasn't my idea, but based on feedback from Andy (and I think Will?). I believe the feeling was that a simple bug had kind of spiraled out of control with a whole nav redesign and that it should be re-focused to be just a fix making My Submissions more findable.

I don't know what the long-term plans are. There seems to be considerable tension between the design team (working on 2.0) and the needs of devs to have a more iterative approach. In any case, the long-term plan will be decided elsewhere. Capturing the "App Validator" requirement in a separate bug is a good idea, I've file that here: https://bugzilla.mozilla.org/show_bug.cgi?id=1041629.

I'll remove "Submit a New App" from the white (secondary) nav since we have it already in the header nav.