The investing app Robinhood is getting blamed for the GameStop fiasco. Its CEO is being called in to testify in front of Congress. Robinhood is an app that makes it simple to trade stocks, options and other derivatives. It’s a huge hit, the most downloaded app on the US app store this year. It’s isn’t available in Ireland so I’ve never used it, but I’ve watched a few videos. It’s very slick. The charts zoom and slide nicely when you touch them. And when you buy a stock, the app rewards you with a pop of confetti.  Congress is annoyed at…