WIP/PoC require.js support

* Updating webassets and Flask-Assets to 0.10-dev.
  **Requires manual fix**.

* Hacking the assets extension to remove the initial "/" to js modules
  otherwise _r.js_ is confused.

* Grouping the invenio.js with bootstrap.js.
  It's a PROOF OF CONCEPT! THINGS ARE GONNA BREAK!!

* Using require.js in dev and almond.js in production.

# Changes

`require.js` (and `almond.js`) are loading asynchronously the modules on dev and handling dependencies between them. Via `r.js` combined and minified files can be created through webassets.

## Libraries

Here, we are using `jquery` and `bootstrap` as dependencies. jQuery supports AMD but bootstrap doesn't which requires the `shim`s (in `settings.js`).

### Own library.

```javascript
define("mylib", ["jquery", "mylib/foo"], function($, foo) {
    "use strict"
    // my code.
    return MyLib
});
```

## Usage

```javascript
// AMD syntax
require(["jquery", "mylib", "bootstrap/dropdown"], function($, mylib) {
    $("[data-derp='herp']").on("foo", mylib.bar)
    return {foo: ...}
})
// CommonJS-like syntax
require(function(require, exports, module) {
    var $ = require('jquery'),
        mylib = require('mylib')
    require('bootstrap/dropdown')

    $("[data-derp='herp']").on("foo", mylib.bar)

    exports.foo = ...
})
```

# Blocked by
- [ ] webassets 0.10 and Flask-Assets 0.10
- [ ] all the crazy JavaScript everywhere...

# Alternatives
- [browserify](http://browserify.org/)
- [jspm](http://jspm.io/)