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/FixedColumn.hs

@@ -22,8 +22,6 @@ module XMonad.Layout.FixedColumn (
         FixedColumn(..)
 ) where
 
-import Control.Monad (msum)
-import Data.Maybe (fromMaybe)
 import Graphics.X11.Xlib (Window, rect_width)
 import Graphics.X11.Xlib.Extras ( getWMNormalHints
                                 , getWindowAttributes
@@ -31,6 +29,7 @@ import Graphics.X11.Xlib.Extras ( getWMNormalHints
                                 , sh_resize_inc
                                 , wa_border_width)
 
+import XMonad.Prelude (fromMaybe, msum)
 import XMonad.Core (X, LayoutClass(..), fromMessage, io, withDisplay)
 import XMonad.Layout (Resize(..), IncMasterN(..), tile)
 import XMonad.StackSet as W