Enhanced the audit trail tests

- Created custom view code for audited memberships
so we can display the group / person name
Groups with memberships can't be deleted
People with memberships can't be deleted
Move delete links to the edit views

- It's misleading to show a delete link
when adding a new record
- Add a confirm prompt to the link
Groups with children shouldn't be deletable
Audit trail shows details of deleted memberships
Display 'name' of deleted group or person
Membership versions can not be undone

- If we let users undo versions of
membership objects we'll encounter
all sorts of problems with stale
associations.
Controller specs for the audit trail

- Ensure that membership versions cannot be undone
Clean up audit trail code

- Make a version object with helper methods
Adding a few line endings