Changed child cardinality of andX and orX to 1..*

In case of a single child the composite constraint will not create a
composite node, but use the child directly.

In case of having more than 2 children, the composite constraint will
append additional constraints as required.

````php
            ->where()
                ->andX()
                    ->eq()
                        ->field('a.foobar')
                        ->literal('foo_value')
                    ->end()
                    ->like()
                        ->name('my_doc')
                        ->parameter('my_var')
                    ->end()
                    ->fieldExists('a.foo') // we can more than two arguments
                    ->fieldExists('a.foo')
                    ->andX()
                      ->eq()->field('f.foo')->literal('bar')->end() // andX works with a single constraint also
                    ->end()
                ->end()
            ->end()
````