copyright header fixes (sigh). some focus management stuff.
Button: better focus manager handling
FocusManager: support for stacking
PopUpManager: modal pop-ups get a new focus manager.
DisplayListWatcher: added examples to the description
IVirtualLayout: docs fix
Button: only listens for keyboard events on focus in
Slider: keyboard controls and focus manager support
Slider: event listener naming
ToggleSwitch: keyboard control and focus manager support
List, GroupedList: keyboard input and focus manager support
Button, Slider, ToggleSwitch: removed focus manager checks in keyDown listeners because they aren't needed.
FocusManager: stores focus when disabled, restores when enabled again.
docs