fix(drawing): draw on right canvas, with photo button hidden
fix(moveCursor): simplify method, since them canvas has 0 offset

To provide offset for cursor image, we add offset of canvas. 'them'
canvas has 0 offset, so it does not matter in addition, so we simplify
function.
feat(cursor): provide scaling of cursor coordinates

Also eliminate cursorX and cursorY vars, and use mouseX and mouseY
instead, because we eliminated 165px offset of video+canvas object.