[Fix #447] Extract ido config into a module

This should make it simpler to disable ido completely if you want to use
an alternative library (like `icomplete` or `icicles` for instance).

sample/prelude-modules.el

@@ -1,5 +1,8 @@
 ;;; Uncomment the modules you'd like to use and restart Prelude afterwards
 
+(require 'prelude-ido)
+;; (require 'prelude-helm)
+
 (require 'prelude-c)
 ;; (require 'prelude-clojure)
 ;; (require 'prelude-coffee)
@@ -9,7 +12,6 @@
 (require 'prelude-erc)
 ;; (require 'prelude-erlang)
 ;; (require 'prelude-haskell)
-;; (require 'prelude-helm)
 (require 'prelude-js)
 ;; (require 'prelude-key-chord)
 ;; (require 'prelude-latex)