[All Platforms][Social] Remove inbox, replace with full two-way messaging

[myself]

Your messaging feature is broken and has been for a long time. The 4 worst problems with it:

- Inbox doesn't work the same way in mobile apps and in desktop.

- It doesn't include the "sent" messages, only the "received".

- You can't search past messages, delete them, archive then, ANYTHING.

- It doesn't sync. "Someone has not yet listened to this". False. She did. "You haven't listened to this yet". False. I did. Only, it was on a different platform and you don't bother to sync the status.

So, please, please, please, fix this broken feature once and for all. How hard can that be?