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,  I wanted you to ask about it :) I have two concerns here:
* Contact renderer appends ```li``` nodes one by one, if we move ```ul``` to the markup, we'll be modifying the element that is in the DOM. Probably using ```documentFragment``` (looks like out of scope for the current patch) or using ```display:none\block``` (not sure how Gecko treats it) can help here.

* It's more general concern I have in mind for a quite long period: is it better to keep all the stuff that is not used at the moment in the DOM (even hidden)? I see we use this technique a lot in SMS, but I don't really feel that it's better than adding some **short living** nodes on the fly and then get rid of it to make DOM tree lighter and cleaner.

What do you think?

P.S. Sorry for the long discussions during reviews :)