Adds a `chat-id` field in `content` map.
The reason it has been added to the map instead of augmenting transit is
that it would simplify the calculation of `message-id`, which in this
case is consistent for both old & new clients.
`chat-id` also represents the `chat-id` with respect of the sender, as
in 1-to-1 chats that is asymmetric.
Signed-off-by: Andrea Maria Piana <andrea.maria.piana@gmail.com>
Andrea Maria Piana
693eae9cf9