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.
Well, don't realдн like that I use Id for the container instead of class. I'd say that styles that I've defined for the ```#messages-recipient-suggestions-container``` can be used by other elements that would like to fill all space between ```To``` field and end of screen (keyboard). But nobody needs it for the moment....