Updated fix for Bug 2170, Adding 'edititems' user-permission

Updated fix for Bug 2170, Adding 'edititems' user-permission

This patch follows up on the addition of the 'edititems'
permission by adding a check of the new permission to places
in the interface which link to the edit item screen.

The catalogue toolbar had to be extensively re-worked in
order to ensure that the "New" and "Edit" menus would appear
(or not) whether or not edit_catalogue, edit_items, or
create_subscription permissions are on.

Revised for current HEAD

Signed-off-by: Colin Campbell <colin.campbell@ptfs-europe.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>