Reworking \OC\Files\Storage\Swift

Full rewrite of \OC\Files\Storage\Swift now using php-opencloud.

That's a working testing configuration for a local DevStack installation:

 ```
        'swift'=>array(
                'run' => true,
                'user' => 'demo',
                'bucket' => 'test',
                'region' => 'RegionOne',
                //'key' => 'test', //to be used only with Rackspace Cloud Files
                'tenant' => 'demo', //to be used only with OpenStack Object Storage
                'password' => 'testing', //to be use only with OpenStack Object Storage
                'service_name' => 'swift', //should be 'swift' for OpenStack Object Storage and 'cloudFiles' for Rackspace Cloud Files (default value)
                'url' => 'http://devstack001:5000/v2.0/' //to be used with Rackspace Cloud Files and OpenStack Object Storage
        ),
```