In assignments with file uploading enabled the Student can use File Picker to upload files

Test Pre-requisites:

• A new 2.3 Assignment with file submissions enabled.

Test Steps:
1. Login as a student and navigate to the Assignment. Click the 'Edit my submission button' and verify that the File manager form element is displayed onscreen.
2. Click 'Add' and verify that the file picker is launched.
3. Select 'Upload a file', choose a file to upload and upload it.
4. Click 'Save changes' and verify that the files have been uploaded.
5. Download the file to verify that the file link has been created properly.
6. Login as a Teacher and download the file, then verify that the file is correct.