Added Handlebars Layout functionality via express3-handlebars module

This restores layout functionality for users who want to use Handlebars instead of EJS by implementing https://github.com/ericf/express3-handlebars as the core rendering engine to delegate to.  

Now, if users set `handlebars` as their default rendering engine in `config/views.js` and point, in `layout` to a default template in `views/layouts`, layout functionality is restored without having to pass partials into every controller action res.view() method.  

Issues:  checks against the property `layout:true` in `config/views.js` need to be set to a default as right now the name of the file is required.