[SMS App] Add support to extract attachments from network packet and send it MMS
Summary
Add support for handling message request packets which have a list of attachments
This MR replaces !205 (closed)
Developer note: When merging this PR, please make sure the final commit's author information says it comes from Aniket since he did 99% of the work here. I basically just rebased his work onto master and fixed merge conflicts.
Test Plan
- Sent message with no attached file from desktop which was sent and received correctly
- Sent message with attached file from desktop which was sent and received correctly
- Sent message with two attached files which was sent and received correctly