Show uploading progress in issue creation popup

Description

When the user opens an Issue Creation Popup and attaches a file, nothing is displayed and the Create button does not work until all attachments have finished uploading.

Reproduce

1. Create a new issue via an Issue Creation Popup, using C key.
2. Attach a file that takes some seconds to be uploaded (1-2mb enough).
3. Click the Create button before the uploaded files have finished.

Current result

Nothing happens and the user does not see the uploading progress.

Expected result

When attaching something to an issue, the uploading progress should be visible to the user. Also, if the user clicks the Create button, the issue might dim and disable the issue edition until the uploads have finished and autocreate on attachments have been uploaded.