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/Layout/Gaps.hs

@@ -35,14 +35,12 @@ module XMonad.Layout.Gaps (
                           weakModifyGaps, modifyGap, setGaps, setGap
                           ) where
 
+import XMonad.Prelude (delete, fi)
 import XMonad.Core
 import Graphics.X11 (Rectangle(..))
 
 import XMonad.Layout.LayoutModifier
 import XMonad.Util.Types (Direction2D(..))
-import XMonad.Util.XUtils (fi)
-
-import Data.List (delete)
 
 -- $usage
 -- You can use this module by importing it into your @~\/.xmonad\/xmonad.hs@ file: