Style Improvements

Continuation of https://github.com/evancz/elm-get/pull/24. 

Manually, I added a `-W` flag, removed unused imports, added a few type annotations and grouped imports by project. Everything else was done by stylish-haskell.

To address the concern about "pretty" imports, I added a stylish-haskell config file to the repo so it will alphabetize imports but only align them in a flat way, not align the names themselves. Anyone else using stylish-haskell in the repo will have the default behavior overriden by the local configuration in the repo.