Bug 17161: Making 'Preview MARC' links show as buttons in batch record modification

Bug 17161: Making 'Preview MARC' links show as buttons in batch record modification

This patch removes the column heading and makes all links show as font
awesome buttons. I have also changed the wording from Preview MARC to
Show MARC to shorten the button and be consistent with other places in
Koha

To test:
1) Go to Tools -> Batch record modification
2) Put in some record numbers and click Continue
3) Ensure column heading 'Preview' no longer shows, and buttons are
showing with an appropriate icon. Confirm button still works as
expected.
4) Confirm button does not wrap on narrower browser

Sponsored-by: Catalyst IT
Works as described
Signed-off-by: Claire Gravely <claire_gravely@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>