Bug 12519 - Convert OPAC list download pop-up to modal dialog

Bug 12519 - Convert OPAC list download pop-up to modal dialog

This patch changes the OPAC list download process so that the download
link triggers a modal dialog instead of a pop-up window. This
streamlines the process a little bit and makes it work better on mobile
devices.

The download list page has been altered so that it works better as a
standalone page, as it might be seen if JavaScript is disabled. Simple
form validation has been added to help prevent submission of the form
without choosing a format.

To test the virtualshelves system preference must be enabled.

- View an existing list in the OPAC and click the "download list" link.
- A modal dialog should be displayed with the download form.
- Submitting the form without selecting a format should trigger either a
  browser-based form validation error (in HTML5-supporting browsers) or
  a JavaScript alert (if your browser doesn't support the "required"
  attribute.
- Choosing a download format and submitting the form should close
  the dialog and trigger the correct download.
- Clicking the "Cancel" link should close the dialog.

Test with JavaScript disabled:

- Clicking the "download list" link should take you to a page which
  contains the same form which appeared in the modal dialog.
- Submitting the form without selecting a format should trigger either a
  browser-based form validation error (in HTML5-supporting browsers) or
  a JavaScript alert (if your browser doesn't support the "required"
  attribute..
- Choosing a download format and submitting the form should result in
  the corect download.
- Clicking the "Cancel" link should return you to the correct list.

Signed-off-by: Aleisha <aleishaamohia@hotmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes QA script and tests, works as described.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>