Report when dist and .stack-work exist

[alanz]

ghc-mod has a heuristic to choose between cabal and stack based projects.

This is (partly) based on the presence of a dist dir, which is taken to indicate a cabal project.

Issue a warning message on startup if both dist and .stack-work are present in the project root.

[alanz]

And we should probably allow the user to be able to explicitly choose/override the project type.

[lukel97]

Related to #963

[lukel97]

Not sure why I removed the good first issue label, seems nice and straightforward!

[samuelpilz]

I could have a go at this.

[lukel97]

I’m thinking sending a showmessage/logmessage notification would probably be a good way to notify the user