Add demo.
Add grunt task `express` to test XHRs.

Start server with `grunt server`
Auto-copy the latest build to demo resources.

For an bleeding edge developing, this auto-copies the final `angular-translate.js` to `demo` directory. That avoids manually editing the demo HTML files.
Support for asynchronous loaders or transformers (basically).

+ Changes all demos
+ Removes completly the old approuch of async loading.

This finally introduces the new `$translateProvider.registerLoader` which automatically can resolve dependencies (via `$injector`), uses promises (via `$q`) and is open for future built-in templates.

`registerLoader` should be *called with an injector-function-argument* -- either a function with dependencies in the argument or with a wrapping array avoiding minimizing issues. The injector-function must return the actual loader function argumented with thr requested `key` only.

```javascript
$translateProvider.registerLoader(function ($http, $q){
        return function (key) {
          ...
        };
});
```

or even

```javascript
$translateProvider.registerLoader(['$http', '$q', function ($http, $q){
        return function (key) {
          ...
        };
}]);
```

The resolving value should be an object structured like (`{key, items}`)
The *return value of the loader function* should be a promise; a `$http`'s promise will be okay if you can garantuee the correct data structure (`{key, items}`).

For sample usage, there are already two simple convenient built-in templates available
1. `registerLoader('lang.php')` which will invoke XHRs for every language switch, i.e. `lang.php?lang=de_DE`
2. `registerLoader({type: 'static-files', prefix: 'lang-', 'suffix: '.json'})` which will invoke XHRs for every language switch, i.e. `lang-de_DE.json`

The demo at `demo/index.html` and `demo/app.js` shows how you have full control about the loader.

related issue #4