Bug 28867: Use Bootstrap button menu and modal for adding patrons to lists

Bug 28867: Use Bootstrap button menu and modal for adding patrons to lists

This patch reworks the controls for adding patrons to a list from the
patron search results page. The <select> is converted to a Bootstrap
dropdown menu, and the list creation form is moved into a Bootstrap
modal.

To test, apply the patch and rebuild the staff interface CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

- In the staff interface, perform a patron search that will return
  multiple results.
- In the toolbar at the top of the search results you should see two
  disabled Bootstrap-styled buttons: "Add to patron list" and "Merge
  selected patrons."
- The "Select all" and "Clear all" links should work to enable and
  disable the toolbar buttons.
- "Clear all" and then check the checkbox next to one of the results.
  The "Add to patron list" button should be enabled.
- Check a second checkbox. The "Merge selected patrons" button should be
  enabled.
- Test the "Add to patron list" button. It should trigger a dropdown
  menu listing existing patrons lists and a "New list" link.
  - Test adding to an exising patron list. It should trigger a message
    at the top of the page which shows a link to that list.
  - Test adding to a new list. It should trigger a Bootstrap modal where
    you can enter the name of the new list.
    - Submitting the list title form should close the modal and trigger
      the display of the message showing how many patrons were added to
      your new list. The link to the new list should be correct.
- Test the "Merge selected patrons" button. It should send the selected
  patrons to the patron merge screen.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>