BitmapFontTextEditor: added selectionSkin to show a highlight behind selected range of text, added support for selecting a range with a click and drag
DefaultFocusManager: handles native stage losing focus on deactivate
BitmapFontTextEditor: selection range updates more intuitively when holding shift and pressing left or right arrow, added support for cut, copy, and paste
BitmapFontTextEditor: support for ctrl+a for select all
BitmapFontTextEditor: handle shift key on touch phase began to select a range