Add self destruct message

[ylecollen]

Reported by @eyallior:matrix.org

[Thatoo]

There is a proposal for synapse server to handle that feature, merged into develop now, here : matrix-org/synapse#6409

So it could be possible soon now, right?

[kojid0]

There is a proposal for synapse server to handle that feature, merged into develop now, here : matrix-org/synapse#6409

So it could be possible soon now, right?

Maybe it'll be implemented in new riotX app as soon as it replaces the old riot app. 😏