Bug 27991: Message field for OPAC problem reporting should have a maxlength set

Bug 27991: Message field for OPAC problem reporting should have a maxlength set

This patch adds a maxlength attribute to the form field for entering
checkout notes in the OPAC, matching the character limit of the database
column. A note is added to show the 255 character limit.

To test, apply the patch and enable the AllowCheckoutNotes system
preference.

 - Log in to the OPAC as a user who has checkouts.
 - On the "Your summary" page, the "Report a problem" fields should
   have a hint below them, "255 characters maximum."
 - Try entering text in one of the fields. You should not be able to
   enter more than 255 characters:

   Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse
   nunc mi, fringilla in mauris quis, hendrerit feugiat mi. Sed ultrices
   mollis nulla sit amet faucibus. Sed volutpat augue risus, eu rutrum
   eros commodo eu. Proin rhoncus nisi vitae magna_

 - Test that your submission is saved correctly.

Signed-off-by: Amit Gupta <amit.gupta@informaticsglobal.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>