Bug 30159: Fix Check() to validate both mandatory and important fields

Bug 30159: Fix Check() to validate both mandatory and important fields

This patch adds a check for both mandatory and important fields when
validating bibliographic records during cataloguing.

To test:

1. Go to Admin -> Biblio frameworks. View the MARC structure of your
   default framework.
2. Search for tag 082. Edit the subfields for this tag.
3. Check the 'important' checkbox for subfield a and Save.
4. Go to add or edit a new biblio record under Cataloguing.
5. Ensure the 082$a field is empty and hit Save.
6. Notice the confirmation pop-up is an unreadable display of HTML.
7. Click Cancel on the pop-up box.
8. Apply the patch and refresh the editor page.
9. Ensure the 082$a field is empty and hit Save.
10. Notice the confirmation pop-up is more helpful this time. Click
    Cancel on the pop-up box.
11. Notice the 082$a field is displayed at the top of the page as an
    important field that is missing information. Use the 'go to field'
    link and confirm this works as expected.
12. Leave 082$a empty and hit Save.
13. This time click OK on the confirmation pop-up. Confirm you are able
    to save your record as normal.

Sponsored-by: Education Services Australia SCIS
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>