Add pop-up with filename to EntityUpload

[matthew-white]

This PR makes progress on getodk/central#589. It adds the pop-up with the filename to EntityUpload.

What has been done to verify that this works as intended?

I added tests, and I also tried it out locally. There was some functionality related to displaying the request status that I wasn't able to verify manually. EntityUpload doesn't currently send any entities, so the request fails immediately. During development, I forced the request status <div> to be visible so that I could style it. That said, we do have tests of this functionality.

One area where we have more limited testing is displaying upload progress. I added tests of the progress prop of EntityUploadPopup, but I wasn't able to test the onUploadProgress callback in EntityUpload and how uploadProgress.value is set in that component. See #127 for related discussion. I think it's OK just to verify this manually: the relevant logic is just a few lines.

Before submitting this PR, please make sure you have:

• [x] run npm run test and npm run lint and confirmed all checks still pass OR confirm CircleCI build passes
• [x] verified that any code or assets from external sources are properly credited in comments or that everything is internally sourced