feat(js2-mode): undeclared face, no semis

Adds a bold to the undeclared variable face, and doesn't complain about
missing semis.
feat(helpers): kill all dired buffers

Adds interactive kill-all-dired-buffers (no keybinding).
feat(smartparens): Add newline if newline after {

Automatically adds an extra newline if { then newline.  Setup for js2,
js and ruby modes.
fix(recentf): up from 5 to 50
Merge branch 'master' of https://github.com/NicolasWinslow/.emacs.d