Bug 837994 - [MMS][User Story] Multiple recipient messaging

Closes gh-9521

commit 40751ef5510cd6fdd56343dcb797db4d3f0b5a5a
commit ab207d5c6f935674619c80333a0203496caa27b4
Bug 869799 - [sms] Receiving two messages at once should not trigger multiple threads of the same id