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.
can you try to not use vh ? It makes reflows very slow when the window is resized (especially when the keyboard is displayed/hidden) (see https://bugzilla.mozilla.org/show_bug.cgi?id=1020469 for more information). In this specific case, you can hide/display the keyboard by tapping on the header for example. This happens too when the attention screen is displayed (eg: receive a phone call, press home, open the sms app and make the suggestion list happen, then cancel the phone call from the other phone).