let user know if CSV upload is ongoing

[huss]

Is your feature request related to a problem? Please describe.

Loading large files via the CSV page can take time. It is unclear to the user that it is ongoing and they should wait.

Describe the solution you'd like

Other places in OED use bouncing balls to show it is working on something that needs to complete. A similar solution seems good here.

Describe alternatives you've considered

None other than no indication as OED currently does.

Additional context

None