Org code block & MMM-mode
1. Org's code block faces improves.
2. Fix wrong face of MMM-mode under dark.
Move defvar backward to avoid some problem.
Fix a problem encountered in latest development version Emacs.

[info] In Emacs 24.3.50.1 , background-color may cannot be changed under GUI Emacs.
Org-mode and Custom
Added face for helm-lisp-show-completion