Outbound MMS Support

[ayyrickay]

Relates to #134. Outbound SMS would be easy to render (for images), but we would need a way to upload files and potentially would need to do some file validation. It's local, so I don't really think it matters, but I don't want the dev phone to crash or something.

We would also need to include an additional field in the SMS API call, so something like a MessageHasMedia() function could be helpful - then we could just conditionally include the media parameter in the api call.