Bug 1072856 - [Messages] Tapping on empty space above send and attach buttons should assimilate currently edited recipient. r=azasypkin

I like the idea using click event handler on ```.content-composer```! Regarding to using id ```#messages-content-composer``` - in the new code we're trying to go away from ids for the elements that aren't really global. So in this case I'd rather use dedicated-css-class-as-js-hook instead ```class="content-composer js-content-composer"``` (see [1]).

[1] https://etherpad.mozilla.org/sms-code-style-guidelines ("JS Hooks")