Uses a less destructive method (the same that Spacemacs uses) than the
one introduced in 13cee68, by introducing MODE-local-vars-hook hooks,
which run after local vars have been initialized.
The old method was to call `hack-local-variables` *before* mode hooks
run, however, this causes variables set by modes to have higher
precedence than local vars, which is unacceptable.
Also moved intero-mode & dante-mode to haskell-mode-local-vars-hook
fd19698927