Check directory file numbers when returning configuration

[tpoliaw]

• Add failing test to demonstrate required behaviour
• Check directory for highest number when returning configuration

Fix for #50

I'm not convinced this doesn't just move the confusion elsewhere. It doesn't give the same get configuration latestScanNumber -> 0 followed by get next scan number -> 42 behaviour but does mean get configuration doesn't return the same configuration you've just set via set configuration.

Maybe get configuration would be better off returning a different type with db_number and dir_number as different fields?

[tpoliaw]

Maybe get configuration would be better off returning a different type with db_number and dir_number as different fields?

configuration field now returns a CurrentConfiguration that exposes a dbScanNumber and fileScanNumber so it is clear when there are discrepancies and there is less confusion around different numbers being returned from configuration and scan.