Build with gulp

I moved everything into ./src, added [./package.json](https://github.com/rschaosid/subrosa-client/blob/08b8ea6a4cb8d8ae4748bd5e4fd92f54702aa086/gulpfile.js) and wrote a [gulpfile](http://gulpjs.com/).

**Advantages**
* css concat+minify in addition to js
* fully automatic build (built index.html uses minified assets):

```
$ npm install
$ gulp build
$ your-browser ./dist/index.html
```

* future needs (png optimization, sprite generation, tests)

**Disadvantages**
* need node and npm
* need gulp (can be mitigated)
* non-built version uses minified versions of vendor libraries (otherwise builds take too long; can be mitigated)

The app still works without doing anything after downloading (you don't have to build it)