rename RenderableMock to SliceMock
clip scale will be center aligned
format code
fix cell animation
add Graphics class to manage all graphic objects
change animation duration to 0.1 second
fix float precision might cause lost last frame when CLAMP_FOREVER
other code clean up
CellRenderer will return Slice
resize will cause redraw of all cells/pieces
but because the width is fixed, nothing will change
add Control class
Label inherits from Control