optionally store chat history (also for otr-conversations)

[lu-x]

and show this history, when resuming a conversation.

[Lukas Matt]

The history and the OTR-keys are stored in the browser (locally).

In case of deleting the local data your are no longer able to decrypt. So there is no advantage in storing OTR messages on the server.

I created a follow-up ID in the vines repo for plain-text archiving.

Thanks for reporting!