Table component should support function or node as emptyText's value

[jihgao]

What problem does this feature solve?

It is requried to put a shortcut link besides emptyText to create a new record in a lot of scenarios. The table component in rc-table support this feature which is restricted to only support strings in ant-design. If you could add this feature, it will make the component more flexable.

What does the proposed API look like?

<Table emptyText={()=>{
   return 'no data';
}}
/>

<Table emptyText={()=>{
   return <div><span>No data</span><a href="">Create a new record</a></div>
}}
/>

[afc163]

PR is welcome~