Added permalink strategies for taxonomies

With permalink strategies the URL of taxonomies can be altered in a way suited to the wished of the site/blog author.

Example configuraton of `app/config/sculpin_kernel.yml`:
```yml
sculpin_content_types:
    posts:
        taxonomies:
            - tags
            - name: categories
              strategies:
                - \Sculpin\Contrib\Taxonomy\PermalinkStrategy\ConvertToLowercaseStrategy
                - \Sculpin\Contrib\Taxonomy\PermalinkStrategy\TranslateSpacesToDashesStrategy
```

Looking for more strategy ideas to add before this is merged so we can give users a good selection.