vouchers need to save to CF periodically
Vouchers need to save to CF periodically the same as we have options for RRD and DHCP leases to avoid losing usage info in an unclean shut down.
Revert "Add voucher backup, configurable from Diagnostics > NanoBSD. Fixes #1087" - voucher db backup already existed under a different name. Ticket is still fixed, just by different code that was already there.
This reverts commit 0d89a2fcac3deea06bdc4a481bbdfae4f18b1ff8.
Set default interval of syncing voucher db to config to 5 minutes instead of 300. Ticket #1087.