Add class Phalcon\Mvc\Model\Metadata\Mongo and Cache

Add class `Phalcon\Mvc\Model\Metadata\Mongo`
Add class `Phalcon\Mvc\Model\Metadata\Cache`

```php
		$di->set('modelsMetadata', function(){
			return new Phalcon\Mvc\Model\Metadata\Mongo(array(
				'mongo' => new MongoClient(),
				'db' => 'phalcon_test',
				'collection' => 'caches',
				'lifetime' => 60,
			));
		});
```
```php
		$di->set('cache', function(){
			$frontCache = new Phalcon\Cache\Frontend\Output(array(
				'lifetime' => 60
			));

			$cache = new Phalcon\Cache\Backend\Mongo($frontCache, array(
				'server' => 'mongodb://localhost',
				'db' => 'phalcon_test',
				'collection' => 'caches'
			));

			return $cache;
		});

		$di->set('modelsMetadata', function(){
			return new Phalcon\Mvc\Model\Metadata\Cache();
		});
```