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.
I discussed this with other people in the past, initially thought like you (and that's why it's like this now) but I'm slowly thinking the other way (after seeing lots of conflicts coming just because of this)