Move lisp files (except init.el) to lisp subfolder.

This is to remove the following warning on emacs 24.4:

Warning (initialization): Your `load-path' seems to contain
your `.emacs.d' directory: ~/.emacs.d/
This is likely to cause problems...
Consider using a subdirectory instead, e.g.: /Users/kaofelix/.emacs.d/lisp
Ignore projectile.cache.