Dialog: Awesome new stacking and overlay implementation. Fixes the following tickets:

Fixes #3534 - Dialog: Modal dialog disables all input elements on page.
Fixes #4671 - Dialog: Modal Dialog disables vertical scroll bar in Chrome & Safari.
Fixes #4995 - Dialog: Modal Dialog's overlay dissapears in IE when content is tall.
Fixes #5388 - Dialog: Don't change z-index when already at the top.
Fixes #5466 - Dialog: "modal" Dialog Incorrectly Cancels Input Events.
Fixes #5762 - Dialog: Get rid of z-index workaround, document it instead.
Fixes #6267 - Dialog: checkboxes that inherit a z-index < jqueryui.dialog z-index don't work.
Fixes #7051 - Dialog: modal prevents tab key from moving focus off slider handle.
Fixes #7107 - Dialog: Modal dialog event loss with high zindex child elements (FF 3.6).
Fixes #7120 - Dialog: Modal operation interrupts drag drop marker functionality on gmaps.
Fixes #8172 - Dialog: Change event cancelled when opening modal dialog from another modal dialog.
Fixes #8583 - Dialog: Mouse event wrongly stopped.
Fixes #8722 - Dialog: Remove stack option.
Fixes #8729 - Dialog: Remove zIndex option.
Dialog: Prevent dialog form losing focus (or move it back in IE <= 8).
Dialog: Save the active element that opened the dialog and restore focus to that. Fixes #8730 - Dialog: Restore focus to opener.
Dialog: Prevent tabbing off any dialog. Fixes #3768 - Dialog: contain focus within dialog.
Dialog: Keep focus inside dialog, even when dialog itself has focus.
Dialog: Use _show and _hide consistently. Fixes #4892 - Dialog: zIndex error with animated modal dialog.
Accordion: Remove deprecated height options. Fixes #5868 - Accordion: Remove clearStyle option. Fixes #5872 - Accordion: Remove autoHeight and fillSpace options.
Accordion: Removed deprecated navigation options. Fixes #5870 - Accordion: Remove navigation options.
Accordion: Removed deprecated icon option. Fixes #6835 - Accordion: Remove icons.headerSelected.
Accordion: Removed deprecated activate method and expanded active option. Fixes #6837 - Accordion: Remove the activate method. Fixes #6853 - Accordion: Remove support for non-number/falsey values for active option.
Accordion: Removed deprecated resize method. Fixes #6839 - Accordion: Remove resize method.
Tabs: Removed ajaxOptions and cache options. Fixes #7147 - Tabs: Remove ajaxOptions and cache options.
Tabs: Removed url method. Fixes #7148 - Tabs: Remove url method.
Tabs: Removed fx option. Fixes #8320 - Tabs: Remove fx option.
Tabs: Removed cookie option. Fixes #7162 - Tabs: Remove cookie option.
Tabs: Removed length method. Fixes #7161 - Tabs: Remove length method.
Tabs: Removed enable and disable events. Fixes #7160 - Tabs: Remove enable and disable events.
Tabs: Removed select method. Fixes #7156 - Tabs: Remove select method.
Tabs: Removed show event. Fixes #7155 - Tabs: Remove show event.
Tabs: Removed select event. Fixes #7154 - Tabs: Remove select event.