Panel re-write

[gabrielschulhof]

Things to keep in mind when re-writing the panel widget:

• Textarea in Panel gets unexpected 140px height style  #6764 - An event needs to be triggered after we remove ui-panel-closed and add ui-panel-open, and autogrow needs to listen for that event, and synchronously call _updateHeight() upon receiving it, because even though a textarea embedded in a panel has non-zero heights (i.e. is visible) while ui-panel-closed is present, the width of its container (ui-panel-inner) is truncated to 0, and under such circumstances height calculations return the wrong (non-zero) value under both FF and Chrome - for some reason. So, the height calculation needs to be performed as soon as the truncation is lifted. For reference look at popup: It triggers popupbeforeposition after it has removed ui-popup-truncate, but before it has removed ui-popup-hidden. Currently, panelbeforeopen is not suited for this purpose, because it is triggered while ui-panel-closed is still present, and other panels rely on this event to become informed of the fact that another panel wishes to open so that they may close themselves.

[apsdehal]

@gabrielschulhof What is the current status of this?