Bug 37309: Improve Delete and Modify items links on the biblio detail page

Bug 37309: Improve Delete and Modify items links on the biblio detail page

The way the "Delete selected items" and "Modify selected items" links
are build on the bibliographic detail page is not nice. We could do
better, for instance using a proper form element instead of building an
URL.

Test plan:
Go to the detail page of a bibliographic record which has several items.
In the items table check some checkboxes and play with "select all",
"clear all" and the action buttons.
Notice that everything works as before.

Minor UI regression that must be fixed: there are CSS rules that cause
problem. When the action links are displayed or hidden the table is
moving up and down.
I think the problematic rules are:
  .btn {
    padding: 6px 12px;
    font-size: 12px;
  }
It makes the UI better if I remove them but still get the bumping
issue.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>