Merge all helpers into a single file

Reduces setup time, since runhaskell is fairly slow to start
Move temporary GHC files out of the way
Add target to clean Haskell build data
Normalize paths
Add unit tests for Flycheck Haskell
Run Elisp tests on Travis CI
Merge pull request #13 from flycheck/merge-helpers

Merge all helpers
get-cabal-configuration.hs: extract also build-depends field as dependencies
Use extracted build-depends to set flycheck-ghc-packages option