Bug 23096: Add floating toolbar to OPAC lists

Bug 23096: Add floating toolbar to OPAC lists

This patch makes the list contents table's toolbar "stick" to the top of
the screen when scrolling. Minor markup changes have been made to enable
this change.

To test, apply the patch and open a list in the OPAC which has multiple
titles on it. Confirm that the toolbar sticks to the top of the screen
when you scroll down.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>