Previously, pressing enter in those text boxes triggered the form to be
submitted. This was rather unintuitive, therefore Enter now triggers the
correct action (add a tag or search for friends).

We cannot add them to image files, because FileResponse may use the wsgi
provided file sending mechanism right when the object is created.
FileResponse does however use the Last-Modified header, which is also
okay.

Depending on the Python version, this might raise an error: Before 3.8,
mimetypes.guess_type could not deal with a pathlib.Path, and only
accepted a string. guess_type is called internally by FileResponse, so
to make sure we don't run into errors, we stringify the path before
passing it to FileResponse.