Add more options

This pull request adds some more options to `grunt-bower-requirejs`. These include

 * `prefix` - Prefix the names of all bower modules
* `aliases` - Rename one bower module to another

They're used like this

```js
{
    'rjsConfig': 'app/config.js' // Path to your app config like always,
    'prefix': 'lib/' // Prefix all bower modules with "lib/",
    'aliases': {
        'eventEmitter': 'EventEmitter' // Rename eventEmitter to EventEmitter
    }
}
```

Which, with the `jquery` and `eventEmitter` modules, would result in something like this.

```js
{
    // ...
    'paths': {
        'lib/EventEmitter': 'bower_components/eventEmitter/EventEmitter',
        'lib/jquery': 'bower_components/jquery/jquery'
    }
    // ...
}
```