Bug 34792: Improve flexibility of CookieConsentBar layout

Bug 34792: Improve flexibility of CookieConsentBar layout

This patch makes CSS and markup changes to the CookieConsentBar, in both
the OPAC and staff interface, so that the layout of custom text and
buttons works better with varying text content and varying browser widths.

The patch also adds some JavaScript to the OPAC so that the cookie
consent bar interacts better with the language selection footer. When
the language selection footer is visible, the cookie consent bar should
"stick" to the bottom of the viewport except when the page is scrolled
all the way down. When the page is scrolled all the way to the bottom
the cookie consent bar should move to the top of the language selection
footer.

To test, apply the patch and rebuild the OPAC and staff interface CSS.

- Go to Administration -> System preferences and enable the
  CookieConsent preference if necessary.
- Follow the link in the preference description to HTML customizations.
- Create an HTML customization in the CookieConsentBar display location.
  Add a paragraph of text.
- Go to the OPAC. If you don't see the cookie consent bar at the bottom
  of the screen you may need to clear your browser cookies and local
  storage.
- Confirm that the text flows well in relation to the buttons: With a
  lot of text, the text expands to fill the width of the cookie consent
  bar and the buttons are below. With a small amount of text, the text
  and buttons should be side by side.
- Test that this layout adapts well to various browser widths.

- Perform the same tests in the staff interface.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>