Make retransmissions in the sync protocol more flexible
Different transports need different retransmission behaviour. Retransmission is currently coupled with key rotation period.
For the Removable Drive we might want cause retransmissions every time that the data for a contact is written to storage.
- user might might not be sure that the file was correctly saved, and on the actual removable drive, and immediately repeat the process
- user might be accumulating data daily for several days before removable drive is eventually dispatched
- drive might soon break or get lost in transit, and user want to repeat the process, retransmitting all messages again (getting them all onto the removable drive again)