Restrict creating groups to only certain subjects

[laurenwalker]

See #1815

[gothub]

If the current user isn't in the list of subjects that can create groups, should the Groups menu item be displayed in the Settings tab?

• if yes, and the My Groups panel will be displayed for a subject that can't create groups, then should the wording be changed for such a user. The wording indicates that the user can manage groups, i.e. "Manage access and permissions to your data with groups..."
• for such a user, Add a new group panel will be hidden
• also, for such a user, the "Create new group" button will be hidden in the My Data tab.

[mbjones]

Again, this is really a DataONE API issue, more than just a MetacatUI issue...