Bug 5357: Follow-up - layout and EAN search

Bug 5357: Follow-up - layout and EAN search

1) EAN search should be hidden if marcflavour is not UNIMARC
2) Fixes layout to match the advanced search in acquisitions
- labels in front of the fields instead of separate lines
- adds a legend to the form and moves the toggle for the search form to it

To test:
- EAN search field should only show up when marcflavour system preference
  is set to UNIMARC
- Check layout is consistent and you like it
- Check toggle for advanced search still behaves the same

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>