Custom table row expansion example

I've added Den's row expander example. I edited the text. The only
other change I made was to disalbe drilldown on the first table because
it is easy to click the wrong thing before you discover the tiny arrow.
Revert "Custom table row expansion example"

This reverts commit 17a5bdd60b0dab19f4c1e73e886d06813f06b8fe.