BDD User Group operations

These changes are implementations of BDD's 'Given' Steps for creating and removing User Groups.
These functions will traverse the User Groups tree and create and / or delete specific User Group(s) depending on if they are or are not found before, in the tree.
```
    $groupLocationId = $parentGroupFound->valueObject->contentInfo->mainLocationId;
    //Search for already existing matching Child Groups
    $query = new \eZ\Publish\API\Repository\Values\Content\Query();
    $criterion1 = new Criterion\Subtree( $locationService->loadLocation( $groupLocationId )->pathString );
```

Can't actually understand why you get the ID from the `$parentGroupFound->valueObject` to load it again on `$locationService->loadLocation( $groupLocationId )`, am I missing something here?