Search over all the fields

If the CKAN search should "know" about all the defined fields of a schema, this extensions should make use of the [`before_index`](http://docs.ckan.org/en/latest/extensions/plugin-interfaces.html?highlight=interfaces#ckan.plugins.interfaces.IPackageController.before_index) method and customize the dict that gets sent to Solr.

This issue is probably related to #54.

Start with CKAN's IPackageController.before_index documentation and inspect how this extension prepares data for Solr. Read related issue #54 for context. Done means the search index includes all fields defined by the schema and those fields can be searched.

Written by the indexing model from the issue text.