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/Commands.hs

@@ -32,7 +32,7 @@ import XMonad.Util.Dmenu (dmenu)
 
 import qualified Data.Map as M
 import System.Exit
-import Data.Maybe
+import XMonad.Prelude
 
 -- $usage
 --