Upgrade to express 4
removed express 3.x related comments
updated express 4.x related packages
Merge branch 'master' of github.com:keystonejs/keystone into express4r3dm

Conflicts:
	lib/core/start.js
	package.json
fixed package.json merge
changed convention for session storage. We now pass in sessionStore which derives from the new express-session module
updated docs script to express 4 conventions
removed warnings raised by express 4
fixed typo
fix for resave on session
Merge pull request #767 from r3dm/express4r3dm

Express4r3dm