Bug 12763: Add more information for users to OPAC Error 404 page

Bug 12763: Add more information for users to OPAC Error 404 page

This patch adds more information to the OPAC 404 error page to make it more user friendly.

To test:

- Apply patch
- Is the information clearly understandable and does it contain all necessary information?
- Native speakers: Is the text correct?
- Non native speakers: Is the text easy to translate?
- Is the HTML correct?

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>