trim typed-transitions dependencies, use QuickCheck 2.12 even on older GHCs, allow STM prior to 2.5

[avieth]

typed-transitions.cabal still had dependencies for packages that it no longer uses. I also got rid of the async dependency by abstracting over a concurrently :: IO a -> IO b -> IO (a,b) for the ping pong example demo.

Besides that, I've been preparing to use the iohk-monitoring package as a dependency, and noticed that a ghc844 build would fail because it chooses by default a more well-supported and accepted QuickCheck < 2.12. We use 2.12 so I added that to the overrides for all GHCs in nix/nixpkgs.nix as well as the required hspec versions to use it.

Also used CPP to allow for stm prior to 2.5. This makes it easier to build on older GHCs and package sets.

[coot]

LGTM

[avieth]

Builds are now failing because the final cachix invocations apparently take more than 10 minutes and don't produce any output. What to do about this?

[coot]

It seems it was stale on pushing /nix/store/wc4chfs9wgi67g1r7im93358h1j6cdkz-ghc-8.4.4. I am actually surprised that this one did not come from nix cache. We could try to update the revision in nix/nixpkgs.nix.