Children and Member tabs show up regardless of edit permission

[bseeger]

In fixing #35, it sort of creates another issue, because of #107.

The "Children" and "Media" tabs each have a button ("Add child", "Add media") to add new nodes or media. The buttons show up regardless of whether or not a user has permission to add Media or Children to that collection. The logic for these tabs is in Islandora module and we may want to override how they work, so they don't show up if the user doesn't have edit access to the parent object.

Because of #107, it makes it easier for a user who shouldn't be able to to add children to a collection. (The access terms field works just fine, btw, as it filters out options the user doesn't have access to. In other words, the user cannot give the new node any access terms they do not have access to).

[bseeger]

Note that this is due to the logic for the tabs being in the Islandora module and the logic for access controls being in Workbench Access. It's just that they are disjoint and can be reconciled.

[birkland]

This is admin-facing, may be candidate to defer to after launch, or not fix at all

[htpvu]

Per Aaron's comment, we wont fix this for now.