Annotated Fixtures

Backward compability: no (but could be added)

Example, how fixtures could look like, if this PR would be accepted:

```php
/**
 * @Fixture("dev", order=100)
 */
class LoadUsers implements FixtureInterface
{
	function load(ObjectManager $manager)
	{
		// some stuff
	}
}
```

or

```php
/**
 * @Fixture(env={"dev", "prod"})
 * Not giving any order could imply order=0
 */
class LoadUsers implements FixtureInterface
{
	function load(ObjectManager $manager)
	{
		// some stuff
	}
}
```

See also #76