Bug 1048362 - [Messages] Compose Panel refresh (highlight actionable part). r=schung

That's too, but the first reason was that in case you change background color on ```messages-container``` you'll notice white ```main-wrapper```'s background when recipients panel going up to the ```singleline-recipients-mode```. That's because ```flex-composer```'s is resizing and parent background is noticeable. What do you think?