Proposed fix for Bug 5106 - Simplify MARC view choices in the OPAC (Conflict marker...

Proposed fix for Bug 5106 - Simplify MARC view choices in the OPAC (Conflict marker fix 2nd try)

- Eliminates the "Extended MARC View" tab
- Points the "MARC View" tab to opac-MARCDetail.pl as it is when XSLT is off
- Offers a "view plain" link on opac-MARCDetail.pl. Clicking this link
  replaces the standard labeled MARC view with an unformatted view similar to the
  one displayed in the pop-up modal MARC view.
- When viewing the "plain view," clicking the "view labeled" link will return
  you to the standard labeled MARC view.
- Adds a new XSL file for displaying MARC data in a slightly-more-formatted
  manner (compared to one big <pre></pre> block).

Removed a conflict marker line from Owen's patch (Marcel).

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>