Add HTML Preprocessors (Jade, Haml and Handlebars)

This implements HTML preprocessors (template engine).

It supports jade, haml and handlebars through [consolidate](https://www.npmjs.com/package/consolidate). Multiple preprocessors can be supported at the same time, it's based on filename extension in `src/app` or `src/components`.

Still to be done:

- [x] Make unit tests pass.