messagelistmodel: support message edition

Handle application/edited-message type to support message edition.
Previous bodies are saved in the interaction to be able to get the
original post to avoid unwanted editions.

While loading a conversation, we store the editions in a temporary
map that we link once the edited message is detected. This work
because we can't edit a message before this message exists.
PreviousBodies in interaction.h contains every previous body detected
and the client can show previous version of the message in a popup.

Deleting a message works the same way, just that any message
with an empty body is not shown.

jami-daemon#316

Change-Id: Ib158abd16ad4b629532de11694e88d86a12d72a8