gulp build

I moved everything into ./src, added [./package.json](https://github.com/rschaosid/subrosa-client/blob/08b8ea6a4cb8d8ae4748bd5e4fd92f54702aa086/gulpfile.js) and wrote a gulpfile (makefile for [gulp](http://gulpjs.com/)).

**Advantages**

* html and css concat/minify in addition to js
* no manual build steps (built index.html already uses minified assets; you don't have to edit it yourself)
* [lint](http://jshint.com/)
* future needs (png optimization, sprite generation, tests)

**Disadvantages**

* need node.js and a lot of npm modules
* build process is less transparent

The app still works without doing anything after downloading (you don't have to build it; just go to ./src/index.html instead of ./dist/index.html).

If you want to be able to build it:

1. install node.js
2. clone subrosa-client
3. `$ npm install`

To build it:
```
$ npm run-script build
```
(or `$ gulp build` if you have `gulp`)