B/I identifiers in 510

[jenniferward]

In 510$c, the identifiers for B/I should be standardized so there is a uniform separator between the year and the sequential number.
The separator should be a forward slash: /
There should be only one separator per identifier.
Examples:
1552/6
1552/31

Note that a variety of separators currently appear in the data:
993120053 B/I 1552|6
990020815 B/I 1552¦31
990000688 B/I 1552|3|6
990001324 B/I [c.1551]¦12
990006917 B/I 1553¦3¦5
993120069 B/I 1553|23

See also rism-international/tasks#834 and #1403 which will also contribute to cleaning up the 510 field.

List of all 510 values: https://docs.google.com/spreadsheets/d/1MB0tTGip5kRSKwHx7byOOp64KkIQ8_EfQ4TPglVvMq8/edit?gid=606910324#gid=606910324