getGroup
Query the server for the latest state of a known group. If no account in signald is a member of the group (anymore), a RequestFailedException with RequestFailedException.errorType: 'UnknownGroupException' is returned.
Parameters
revision
The latest known revision of the group, default value (-1) forces fetch from server
Throws
if signald sends an error response or the incoming message is invalid
if the request to the socket fails