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

* I think it would be more correct if you move that code to ```Compose.js``` as one more source for Composer ```interact``` event [1];
* Could you please also check if we can remove ```click``` event listener for attach button [1] since we have it on parent ```.js-content-composer``` element?
* Could you also add appropriate unit test for the change [2]? 

[1] https://github.com/azasypkin/gaia/blob/8f452cbfb9049ffab7adc5c9283d373fbbbedafd/apps/sms/js/compose.js#L364
[2] https://github.com/azasypkin/gaia/blob/8f452cbfb9049ffab7adc5c9283d373fbbbedafd/apps/sms/test/unit/compose_test.js#L1946