Bug 875836 - [MMS] Group message sender display DRAFT

This draft is for review only cc @gnarf37 

https://bugzilla.mozilla.org/show_bug.cgi?id=875836

Current output:

<img src="http://gyazo.com/fb4c7179aefce60ae85008bfb62507af.png">

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>