HapiJS integration

This PR sets up a web application using HapiJS, a production ready and growing alternative to ExpressJS for NodeJS application development. Hapi is compelling because it is configuration-centric, modular and with off-the-shelf solutions fit to our use case (caching, authentication, batch requests, scalability). Like Express, it doesn't impose a project structure so we are free to organize our application in the sanest way we see fit. It was developed by the creator of [OAuth](http://en.wikipedia.org/wiki/OAuth), and has been used in huge scale production projects (it supports Walmart's entire mobile infrastructure and served them over Black Friday).

This PR also sets up automatic assets compilation using GruntJS tasks, although if you two are interested in [GulpJS (a build system that uses streams)](http://gulpjs.com/), it is probably easy enough to switch build systems.

Other dependencies:
*  node-sass: a Node.js wrapper for [libsass](http://libsass.org/), a C/C++ implementation of Ruby SASS that is orders of magnitudes faster

Notable absences:
* Any client-side JavaScript frameworks/libraries
* Script loaders, minifiers, assets strategy for JS
* Test framework and tests (not much to test right now)

Coming
* Bower integration for management of client-side packages
* Browserify integration?

@hakubo and @federico-lox