Ability to delete floating groups

[Tanya Prokrym]

We would like the capability to delete floating groups. This is especially important during initial setup and testing of floating groups within a consortium.

The ability to delete floating groups would have to:

1. check to ensure no existing items are using the 'selected' floating group rule. If an item is using the rule, a warning should appear. The deletion of the rule should not be allowed.

2. check for the admin_float_groups permission which could be used for this feature. I think a separate delete_float_group permission would be best though.