Files & Uploads filtering (DOC-1316)

@martynjames @marcotuts @mhoeber @srpearce @lamagnifica please review
This is an initial draft. Still need to replace outdated screenshots; waiting for finalized UI.
"from a component, from a course update, or in the course handouts"

"On the **Files & Uploads** page, the **URL** column lists the Studio URL and the web *(lowercase)* URL for each file."