Bug 10751: standardize validation of title in staff purchase suggestions form

The form for adding a new purchase suggestion in the staff client
indicates that the title field is required but does nothing to enforce
this rule. This can be handled client-side with HTML5 validation
attributes and Koha's built-in validation plugin. This patch implements
this.

To test, apply the patch and go to Acquisitions ->
Suggestions -> New purchase suggestion. Try submitting the form without
entering a title. Doing so should trigger a validation warning.

Submission of the form with valid data should work correctly. Editing an
existing suggestion should also work correctly.

The patch displays a message 'Required' near the title field.
After submitting a empty title it changes to 'This field is required'
Signed-off-by: Marc Véron <veron@veron.ch>

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
The title field is required since commit
d565fb02e9fca2ac9c506e4e7d44fd8b0d66f06a
This one makes it more consistent with formatting. It makes sense.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>