[#6777] Added site-wide notification banner

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6777] Fix notification seen count, always display close button, slight HTML structure change

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6777] Use single site-notification cookie and improve performance / logic of in/active notifications

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>