constructor(props) {
    super(props);
    this.state = {
      isMoving: false,
      isResizing: false,
      startProps: null
    };
  }
@constructor

@property {string|Element} title content to display in the title bar.
 If empty, the title bar will be hidden.
@property {number} x position from the left in pixels
@property {number} y position from the top in pixels
@property {number} width width of the panel
@property {number} height height of the panel
@property {string} [className] additional class name for the container
@property {number} [parentWidth] width of the parent window
@property {number} [parentHeight] height of the parent window
 If parent window size is specified, the panel cannot be moved outside of its bounds.
@property {boolean} [minimized] whether the panel is minimized (show only title bar)
@property {boolean} [movable] whether the panel can be moved, default true
@property {boolean} [resizable] whether the panel can be resized, default false
@property {boolean} [minimizable] whether the panel can be minimized, default true
@property {function} [onUpdate] callback when user move/resize/minimize the panel
@property {function} [onMoveEnd] callback when user stops moving the panel
@property {function} [onResizeEnd] callback when user stops resizing the panel