Authorize access to admin panel, etc.

Adds a separate admin namespace and base controller, with authorization
by looking up the admin property in the user's LDAP account.

spec/views/admin/dashboard/index.html.erb_spec.rb

@@ -1,5 +1,5 @@
 require 'rails_helper'
 
-RSpec.describe "ldap_users/index.html.erb", type: :view do
+RSpec.describe "dashboard/index.html.erb", type: :view do
   pending "add some examples to (or delete) #{__FILE__}"
 end