Slow expanding of rows if a table is used in it

Hi there,

I got a strange issue when I'm putting a sub table in an expanded row of a root table. I wrote a little POC (https://github.com/CroniD/react-bootstrap-table-big on branch `master`) which you can use to reproduce this.

If one tries to expand/collapse a row, the browser gets a big lag. The lag gets bigger for each row, so I think when an expansion is triggered, the component loops through all rows of the root table.

Best regards