Support destroyOnHide

[aight8]

rc-trigger support this, but I want to use rc-dialog as standalone component for errors. So it were nice when this option were possible on rc-dialog level already.

[yiminghe]

Just render null

http://react-component.github.io/dialog/examples/ant-design.html

[yesmeck]

@afc163 可以考虑加这个，一来在内部控制 unmount 可以解决 React 16 render null 的时候会没动画，二来 Modal 内部的组件可以比较方便的使用生命周期。

[afc163]

对，Modal 清空数据是老大难问题

[yesmeck]

Trace in ant-design/ant-design#8494