Create category for year-less pins

[BrightRaven]

We have no way to assign a pin a label for having no year. Some pins are traded at globals every year such as the volunteer pins. We need a special category for these and they should probably display at the bottom of the list of pins by year.

Suggested names for this category:
Year-less
General
Unassigned
Un-dated
No Date
No Year Specified

[scytherswings]

Currently the way to do this would be to use an empty year. This is already supported on the backend.