Ability to destroy Private Rooms and Messages where users are from the same home server.

This issue has been migrated from [#1647](https://github.com/matrix-org/synapse/issues/1647).

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It will be good to have the ability to destroy Private Rooms and Messages where users are from the same home server. On creating a room or sending a message, it will be good to have timed destruction OPTIONS: On Read within 5 mins, 1 Hour, 1 day, 1 week (need not have been read for 1 hour, 1 day or 1 week options). I should be able to set this even after sending a message or creating a room ( if I am admin). This is for pictures and videos shared as well. There should be no trace of this in the server even for admin of HS. Make sure to give it as an API control as well.

It is very important that this part of the Mobile UI on Android and iOS not just web.