Bug 1011604 - [Messages] Update to use <gaia-header>

Got it, so if it's not related to gaia-header, it would be better if you move it to your patch with "+" button. MoreoverI haven't tested "To:" field with this patch :D 

I'm asking this because we had a bunch of problems with this field recently: lost focus, janky transformations, unwanted reflows that were caused by not really obvious things, so it really needs attention.