Make it harder to accidentally delete an attribute definition that is in use

Similar to GRP-2852 which was for Attribute names. In the attribute assignments for an object, to delete the assignment you need to open a menu and choose delete. Before opening the menu there are two links for the attributeDef and the attributeDefName. Either of these links takes you to the attribute def or name page, where you can delete that instead. There is a warning, but a user could ignore it, thinking it's just to warn about deleting the assignment.

If you delete the attribute def, it does very bad things. It will delete all the attribute names using it, and all the attribute assignments for all those names. And if it is a wheel member doing it, there is no way to make it read only to protect it.

Once attribute defs are set up, it's not a common task to want to delete it. There should be an option to prevent its deletion in the UI, and make the admin use GSH if they want to really delete the definition.