Bug 15527: Add a stylesheet for OAI-PMH to aid usability

 Bug 15527: Add a stylesheet for OAI-PMH to aid usability

This patch introduces an XSLT file grabbed from DSpace and a couple
css files.

To test:

- Point to your dev Koha's oai endpoint. For example:
  http://localhost:8080/cgi-bin/koha/oai.pl?verb=ListMetadataFormats
=> FAIL: Look how ugly it is for humans.
- Apply this patch
- Reload
=> SUCCES: It is styled and provides really useful links to interact with
  the OAI server verbs.
- Sign off :-D

Sponsored-by: Universidad Empresarial Siglo 21
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
  Works as described. Nice looking.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>