implement aborting a file upload

fixes CNVS-16087

Adds the ability to abort a file that is currently being uploaded.

Test Case

Given your on new files
When you attempt to upload a large file
Then you should see a clickable x next to that files progress bar
And clicking it should abort the upload
And the file progress should be removed from the view

Change-Id: I39858e075beeaedc1499a5a3a8ed21aae541d116
Reviewed-on: https://gerrit.instructure.com/42332
Reviewed-by: Dan Minkevitch <dan@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>