add ability to delete file/folder to new_files

closes: CNVS-14726
refs: CNVS-12727

test plan:
* go to new files,
* click the cog at the right end of the row,
* click the "Delete" option
* it should disappear
* reload the page, make sure it is still not there

Change-Id: Ieb6d1246885e1e7f4709bd6b2946fa58d8f3cdec
Reviewed-on: https://gerrit.instructure.com/39157
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>