Amend scanner scheduling: Handling ScanError msg

[bertllll]

(First phase)

If anything from the scanning goes wrong on the side of the BlockchainBridge, severe enough to halt the process, it results in a message called ScanError and addressed to the Accountant. So far what we've ever cared of was that we just canceled the scan inside the Scanners, which is important for being able to run a new scan in the future as it cannot be done until there is a timestamp stored in the respective scanner that signifies the time when an ongoing scanner begun. We do this still, but with the late big redesign in the scan timings and scheduling, we have now a responsibility to sustain the continuity of the constantly rescheduled scans and this is possibly a place where we could suffer discontinuity unless we make sure we will schedule a new scan when we receive this ScanError message.
This part, the responsible rescheduling is missing now and it would be fatal to the scanners, as there would be no other force to awake the scanner again.

The bottom line: add scheduling.