Flexible Haskell - a new plugin for JetBrains IDEs

Both actually. Because of our Psi-Structure, I was able to add a formatter myself. It wasn’t working great until yesterday though (as in: it was functional, but could have been better) and still needs polishing here and there. I also added some support for other formatters like ormolu, fourmolu and stylish-haskell (that you should have been able to select under settings), but I am reviewing all of that again, because I didn’t properly test them before and found a few bugs with them. I am also adding hindent while at it. Do I miss any popular ones?