Bug 840076 - MMS download options. r=crh0716.

Reopen the mms panel in settings, and add mms download option selector.
Merge pull request #9526 from steveck-chung/settings-mms-panel

Bug 840076 -  [MMS][User Story] MMS download options. r=crh0716.
- Reopen the mms panel in settings, and add mms download option selector.