Bug 1034600 - [Messages] Suggestions list is badly located. r=julien

* Recipient suggestions container moved to more appropriate place;
* Recipient suggestions now occupy all possible space minus heights of the app header and message "To" field.
* ```.contact-list``` styles are cleaned up a bit.
long discussions is what makes a common thinking inside the team so it's good :)

* I think using a documentFragment is the way to go here (and yes, maybe the `<ul>` removal can be in another non-blocking bug as you suggest, to minimize risk)
* I think the other way because I think adding/removing nodes on the fly has several inconvenients:
  * makes the code bigger and more complex (see here where we need to add the event handlers on the fly too)
  * makes it more difficult to style in the browser (when the markup exist you only need to add the "display" CSS attribute with the devtools)

  and few advantages:
  * less DOM so faster refreshStyles operation => I don't think this has a real performance implication, one or few nodes won't make any real difference
  * I don't find other advantages :)