Should be able to use "Media Tab" without having field_member_of

[rosiel]

Title (Goal)	Have the option an Islandora content type that doesn't have field_member_of
Primary Actor	Repository admin
Scope	Architecture
Level	High
Story	As a repository admin, I want to make new content types that work with Islandora. I want to make the decision about whether a content can "have media" separately from whether that same content type can "be a member of" another node. For example, I might use taxonomy terms for organization. I want the option to not add field_member_of to my Islandora content.

Relevant architecture and proposals for how logic could work:

• in the access() function that determines whether the "Members" tab appears, ManageMembersController currently requires both field_model and field_member_of be on the node.
  • Instead, this should check whether any nodes have 'field_member_of' which can be pointed to this content type.
• In the access() function that determines whether the "Media" tab appears, ManageMediaController currently requires both field_model and field_member_of to be on the node.
  • I propose we rename the configuration option in the Core Islandora Settings, currently displaying Fedora URLs for selected bundles, to be a more generic "which content types are Islandora" setting, and use that to determine whether the Media tab should display on nodes.

Making these changes, Islandora Defaults would still work the same.