Correct contextual send language.

1) Use "secure" and "insecure" vs "encrypted" and "unencrypted.

2) Use MMS instead of SMS where appropriate.

Fixes #1602
Validate MMS delivery destination.

We can't depend on validated Recipients anymore, so this adds
parity to the validation the SMS transport does now.

Fixes #1592
Fixes for outgoing SMS/MMS direct and fallback behavior.

1) Correct MMS fallback settings.

2) Prevent SMS/MMS messages from leaking out under certain
   circumstances when they shouldn't.
Fix UI side of broken MMS fallback.

1) Actually tell the SendReceiveService to send the MMS if it is
   one.

2) Display the correct string (SMS vs MMS) in the fallback dialog.