Bug 22274: (follow-up) Use one CSS file for SCO and SCI

Bug 22274: (follow-up) Use one CSS file for SCO and SCI

This patch makes the self-checkin CSS created in Bug 22638 the CSS for
self-checkout as well. The interfaces have the same requirements.

This patch also replaces some old image-based icons with Font Awesome
icons.

To test, apply the patch and rebuild the OPAC CSS. Clear your browser
cache if necessary.

 - Enable both self checkout (WebBasedSelfCheck) and self checkin
   (SelfCheckInModule).
 - Test both interfaces, confirming that the style is consistent for
   each and looks correct.

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>