Add ability to display all unused Tag values and bulk delete Merged

Because non-administrative user accounts are not able to delete Tag values created by mistake, the Aha administrator needs to periodically cleanup the Tag values to remove values that are not being used. It would be helpful to have a checkbox for "show only unused values" in the Tag list and also have a Delete All button.

In addition, it would help to give non-admin user accounts the ability to delete Tag values for the account that created and also if it's not being used. As-is, users who create a value by mistake (typo, want different wording, etc.) they either have to contact the admin to correct the mistake or wait for the admin to do periodic cleanup.