Use dash-notation instead of camelCase in emacsPackages.otherPackages.

Package.el's convention is haskell-mode, not haskellMode. Rename the
'manually' managed packages in Nix so we don't have duplicates in case
a package is in package.el and in `otherPackages' (in which case the
newer version will be picked automatically).

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>