With this commit we add two new RPCs for handling sidecar tickets.
ListSidecars will show all sidecar tickets known to the local database,
including those where our node is on the receiving end of a sidecar
channel.
CancelSidecar will cancel a specific sidecar ticket. If an order was
created for it, that bid order will be canceled. Doing so will make sure
the ticket isn't executed any further.
To make it possible to decode a sidecar ticket through RPC instead of
only relying on the output of the CLI, we add the DecodeSidecarTicket
RPC method to the trader daemon.
