Fixed|UI|Client: Don’t allow dialogs to grow higher than the view

For a dialog that has a downward opening direction, don’t let the
dialog’s height to be taller than the available room below the
anchor.
UI|Client|ScrollAreaWidget: Scrolling can be disabled
UI|Client: Dialog and popup improvements

Adjusted the position of dialog buttons and the content height.
Also, open dialogs eat mouse wheel events in addition to button
clicks.
UI|AlertDialog: Adjusted list behavior

The list of alerts is scrollable, and the latest alert appears at
the top of the list.