This adds ability to refresh the list of uploaded videos without refreshing the whole page.

Added a refresh button that when clicked:
- fetches a fresh list of uploaded files from the server
- updates `PreviousVideoUploadListView`
- removes the successfully completed uploads from `ActiveVideoUploadListView`
- retains the ongoing or failed uploads in `ActiveVideoUploadListView` so that they can be monitored/retried

The view can also be refreshed without user action, but I felt it may be less surprising to have a button instead.

MA-333 update: auto-refresh list, fix test failure

Changes:
1. Refresh of file list triggered by upload completion. Refresh button retained and label changed to "Refresh List".
2. Added `aria-live="polite"` to `.active-video-upload-list` and `.assets-table`.
3. Removed unused parameter `evt`.
4. Added self to the `AUTHORS` file.

MA-333 update: added tests

MA-333 update: removed refresh button

MA-333 update: address review comments of @mushtaqak

MA-333 update: simplify nested `_each`

MA-333 update: rename viewRefresh to isViewRefresh

MA-333 update: doc string for `clearSuccesful`

MA-333 update: fix accessibility

MA-333 update: update only successfully uploaded videos

MA-333 update: use window.SR feature to notify screen readers that video upload was successful (@pomegranited)