New module: XMonad.Prelude

This is a convenience module in order to have less import noise.  It
re-exports the following:

  a) Commonly used modules in full (Data.Foldable, Data.Applicative, and
     so on); though only those that play nicely with each other, so that
     XMonad.Prelude can be imported unqualified without any problems.
     This prevents things like `Prelude.(.)` and `Control.Category.(.)`
     fighting with each other.

  b) Helper functions that don't necessarily fit in any other module;
     e.g., the often used abbreviation `fi = fromIntegral`.

XMonad/Actions/Launcher.hs

@@ -18,10 +18,9 @@ module XMonad.Actions.Launcher(
   , launcherPrompt
 ) where
 
-import           Data.List       (find, findIndex, isPrefixOf, tails)
 import qualified Data.Map        as M
-import           Data.Maybe      (isJust)
 import           XMonad          hiding (config)
+import           XMonad.Prelude
 import           XMonad.Prompt
 import           XMonad.Util.Run