[MEDIA] File downloader now in PHP, added proper name in the UI and changed the forma...

[MEDIA] File downloader now in PHP, added proper name in the UI and changed the format for new attachment file names

The file downloader was changed from a simple redirect to the file to one
implemented in PHP, which should make it safer, by making it possible disallow
direct access to the file, to prevent executing of atttachments

The filename has a new format:
  bin2hex("{$original_name}")."-{$filehash}"
This format should be respected. Notice the dash, which is important to distinguish it from the previous
format, which was "{$hash}.{$ext}"

This change was made to both make the experience more user friendly, by
providing a readable name for files, as opposed to it's hash. This name is taken
from the upload filename, but, clearly, as this wasn't done before, it's
impossible to have a proper name for older files, so those are displayed as
"untitled.{$ext}".

This new name is displayed in the UI, instead of the previous name.