use helmet module to more secure application

Helmet module is the middleware to add security headers for Application.
I think these headers is so important for security that we should also use in MEAN.js.

We need to install the latest one from github currently because it looks old on the npm site.
The old one is not working on my local MEAN.js stack.
keep enable Cache-Control

helmet.defaults() disabeles Cache-Control. I guess it's controversial to disable it.
Fixed locals.cache when NODE_ENV==='production'
Move license to it's own file.  Easier to see what the license is when first encountering the repo
Update README.md to include where to download the MEAN.JS boilerplate
Merge branch 'pr/23' into 0.2.3
Fixing License and Readme
Fixed Comments and README
Merge branch 'pr/15' into 0.2.3
Finalizing the User Accounts Module
Adding Comments
Adding Accounts View
Merge branch '0.2.3'
merge upstream 0.2.3
workaround for express 4 connectMongo session bug
Add check of password and salt in user auth
Merge branch 'pr/25'
Adding the salt part to the hashPassword FN
0.3RC

Express 4 Support
New naming convention
Glob patterns
CSS Linting
Uglify
CSS Min
Environmental Asset Management
DI Menu System
Merge branch 'pr/18' into 0.3.0

Conflicts:
	app/routes/core.server.routes.js
	config/express.js
	package.json