resets pages keys after sorting to numerical values

I want a simple next/previous page navigation in a blog setup with:

    {% for page in pages %}
        {% if current_page == page %}
            {% if pages[loop.index0 + 1] is defined and pages[loop.index0 + 1].meta.date %}
                {% set divider = 1 %}
                <a href="{{ pages[loop.index0 + 1].url }}">
                    {{ pages[loop.index0 + 1].title }}
                </a>
            {% endif %}
            {% if pages[loop.index0 - 1] is defined and pages[loop.index0 - 1].meta.date %}
                {% if divider %}
                    –
                {% endif %}
                <a href="{{ pages[loop.index0 - 1].url }}">
                    {{ pages[loop.index0 - 1].title }}
                </a>
            {% endif %}
        {% endif %}
    {% endfor %}

in the template file.

Alas that's not possible because Phile has no next/previous page property and the `pages` keys aren't integers after the the [sorting in Page.php](https://github.com/PhileCMS/Phile/blob/master/lib/Phile/Repository/Page.php#L97) and so `loop.index + 1` does not work. Reseting the array keys after the sort should fix that and make the previous/next page accessible by loop.index+/-1.