Bug 15314: Use Bootstrap modal for cataloging merge MARC preview

 Bug 15314: Use Bootstrap modal for cataloging merge MARC preview

In order to reduce the number of dependencies for common interactions we
should attempt to use Bootstrap modals in place of Greybox ones.

This patch modifies the cataloging merge selection page so that the
MARC preview is shown in a Boostrap modal. This patch also changes the
preview link to be the text "View MARC" so that it is clear what it
does.

To test:

1. Apply the patch and navigate to Cataloging.
2. Perform a search which will return results from the catalog.
3. Select two records and click the "Merge selected" button to begin the
   merge process.
4. Test the "View MARC" link for both merge choices and confirm that the
   correct data is shown each time.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised

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