Implicit grant now handles scope like password grant, keys and tokens are now case-sensitive

http://tools.ietf.org/html/rfc6749#section-4.2.1

The scope should be pulled from $authParams['scope'] (without an s). The scope should also be handled the same way as the other grants.
this entire `foreach` block can be replaced with:

```php
$scopes = array_filter($scopes);
```