Dialog: Switch back to shuffling z-index, but only look at .ui-front siblings.

Fixes #9166 - Dialog: moveToTop implementation resets flash/video/iframe/scroll
Fixes #9364 - Dialog: Click of element with tooltip scrolls the dialog to the top
Day TH's: scope=col. Closes gh-1074

A TH must feature a way to know which span of TD's it applies to, and in simple tables such as date tables, this can be achieved through the use of the scope attribute.