[Feature] PDA messenger quality of life updates

[glassofmilk]

https://github.com/goonstation/goonstati...6/pull/139

This pull request includes two updates to the PDA messaging system:
- The list of other PDAs is now alphabetized by first name
- The from line of a PDA message will now include the sender's assignment, if it exists, and the group the message was sent to for group texts