Bug 884890 - [sms] we're scrolling the recipients too low

- Removes unnecessary margin
- Scrolling to top of list will match bottom edge of last visible recipient
- Scrolling to bottom of list will match bottom edge of last recipient in list
- Scrolling to bottom of list will reveal bottom edge of an "out of view" recipient (as shown in visual design specs)

https://bugzilla.mozilla.org/show_bug.cgi?id=884890
Signed-off-by: Rick Waldron <waldron.rick@gmail.com>