reimplements mask using the new input lib, makes mask use a solid color
(masks shouldn't become darker the more you draw over itself) and the
mask layer is now rendered with the alpha using css.
Signed-off-by: Victor Seiji Hariki <victorseijih@gmail.com>
Implements command pattern for providing edit history capabilities to
editing. For now, no implementation is done to support keyboard
shortcuts, so the buttons are the only way to navigate. Also, only image
insertion is supported for now. Waiting for the masking updates to
implement masking history.
Signed-off-by: Victor Seiji Hariki <victorseijih@gmail.com>
