Stable Haskell Version

[angerman]

To reduce confusion with upstream, we should clearly mark our releases to be Stable Haskell releases. Currently GHC returns

The Glorious Glasgow Haskell Compilation System, version 9.14

we probably want

The Glorious Glasgow Haskell Compilation System, version 9.14 (Stable Haskell YYYY.WW)

Where YYYY and WW are the Year and Week Number of the stable haskell release.

As we are tracking upstream, we'd be just creating rolling time based releases ontop of upstream branches.