Draw the MultiButton into its canvas context using the current .__value property and multiButton style.
@memberof MultiButton
@instance
function draw() {
    this.ctx.fillStyle = this.__value === 1 ? this.fill : this.background;
    this.ctx.strokeStyle = this.stroke;
    this.ctx.lineWidth = this.lineWidth;

    var buttonWidth = this.rect.width / this.columns,
        buttonHeight = this.rect.height / this.rows;

    for (var row = 0; row < this.rows; row++) {
      var y = row * buttonHeight;
      for (var column = 0; column < this.columns; column++) {
        var x = column * buttonWidth,
            _buttonNum = row * this.columns + column;

        this.ctx.fillStyle = this.__value[_buttonNum] === 1 ? this.fill : this.background;
        this.ctx.fillRect(x, y, buttonWidth, buttonHeight);
        this.ctx.strokeRect(x, y, buttonWidth, buttonHeight);
      }
    }
  }