[WIP] a new topics concept

This PR includes:

- [x] - Topics API (link, unlink, search, post, get all, get single)
- [x] - New implementation of the topics in the admin panel based on AngularJS
- [x] - upgrade, core SQL scripts for new topics tables
- [x] - Specs
- [x] - CSRF token validation via AJAX calls (http://www.corneliu.it/symfony-2-5-csrf-token-ajax-calls-twig-custom-function/)

Example usage in twig:
```
<script>
    var token = "{{ default_csrf_token() }}";
</script>
```
Shouldn't this be: findAllParentChoices