Support for Wider Range of Touch Events

Added support for IE's pointerdown and mspointerdown to the custom
"clicktouch" event, since IE does not support touchstart touch events.
The clicktouch event is currently only utilized by CZ's top right menus,
but could be plugged in anywhere the standard mouse click event is used.
e.g. Touching an exhibit to zoom in.
Improved Start-Up Display

Added some initial CSS styling for splash overlay directly to cz.html so
that it immediately hides the entire page. The main splash styling,
along with the rest of the site's CSS, is loaded via JavaScript, which
can sometimes lead to cz.html unstyled content being briefly displayed.
Merge branch 'NeilCresswell-ie-touchscreen-fix'