Add a sub-generator for creating a new layout

[dcalhoun]

While prototyping it could be helpful to have a sub-generator that produces a new page and layout. This feature would speed up the process of starting a unique page in a prototype. The command would need to accept a "name" parameter, and would generate the following:

• _layout/[name].html
• styles/[name].scss
• scripts/[name].js
• [name]/index.html

The layout file would ideally automatically include the Sass and JavaScript file.