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.
Namespaces in *uses*

```
use eZ\Publish\API\Repository\Values\Content\Query;
use eZ\Publish\API\Repository\Values\Content\Query\Criterion;
```

then you can do it like:
```
    //Search for already existing matching Parent Groups
    $query = new Query();
    $criterion1 = new Criterion\Subtree( $locationService->loadLocation( self::USERGROUP_ROOT_LOCATION )->pathString );
    $criterion2 = new Criterion\ContentTypeIdentifier( self::IDENTIFIER_USER_GROUP );
    $criterion3 = new Criterion\Field(
        'name',
        Criterion\Operator::EQ,
        $parentGroup
    );
    $query->criterion = new Criterion\LogicalAnd(
        array( $criterion1, $criterion2, $criterion3 )
    );
```