The texts around adding files and subtitles are not user-friendly

Logged in as 422196@mail.muni.cz:

Reproduction steps:

1. Open an existing project and go to the "Files" section
2. Click on the "Undefined" (to add a Film file - the weird field name is tracked in #237 (closed) )

Expected result:
The newly added files are named as they were on upload, so that the users see what they uploaded.
There are buttons for deletion of the film and the subtitle.

Actual result:
The files are named as gibberish.
There is a generic "Delete the artifact" button - what does it do? What is an artifact? (Yes, the user encounters it during creation, but doesn't know much about it - and if you spend a few minutes searching for files and confirming things before submission, you can easily forget - I did). Does it delete both the film and subtitles?
Is it not possible to delete only the subtitles, or only the film? (See #43.)

This is the case for the other fields as well, users can e.g. easily get confused during uploads of multiple cover photos.