Added propertyaccessor based multisort

- Twig extension
- Static method

````jinja
{% for foo in content.foos|sulu_util_multisort('[title]', 'asc') %}
    {{ foo.title }}
{% endfor %}
````

Sorts arrays or objects, on properties or methods thanks to the [PropertyAcessor](http://symfony.com/doc/current/components/property_access/introduction.html)
__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | n/a
| BC Breaks     | n/a
| Doc           | 
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