transfer the dock bar containers when docking a window
update the dock bar

This adds some query methods, and sends change events to the parent dock
area.
update the dock area

this exposes the dock manager query methods.
update the dock window

this shifts the logic for automatically closing a dock window to the
dock window itself. The window remains open unless the child dock area
is completely empty of all content and dock bars.
clip the slide out size to the pane size