add reactjs modal to admin cog

fixes #CNVS-14256

One the new files page written in reactjs, the file and folder item
admin cog has a 'restricted access' option. When you click this, a
modal should appear. It now does.

Test Plan
Given you've enabled the new files page for a course
As a teacher
When you navigate to the files page
You should see an admin cog when you hover over a file or folder
Then clicking on the admin cog should show you a list of options
And when you click on 'Restrict Access"
Then it should show a modal
And clicking the modals x should close the modal
And clicking the modals cancel button should close the modal

Change-Id: Id8358a35ed0d7c23ff98227af655a88a459d9174
Reviewed-on: https://gerrit.instructure.com/37791
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>