[library] Require Admin Access to see Library Manager Page

[PlasmaIntec]

Related to #86, we should eventually separate the Admin and Instructor roles as only the Admin should be allowed to access the Library Manager Page.

[sballance]

I'll go ahead and take this issue.

[sballance]

@PlasmaIntec @dakriy are we wanting to limit this to only superusers or should instructors be able to see it as well? I was originally just allowing superusers to access the post routes but I thought it would be a good idea to check before continuing. I don't want to allow instructors to access the page if they can't submit the post request.