Query Trailblock Description

This allows us to have more control over our queries to the content api.

The following has changed:
* Query is now defined in the TrailblockDescription and not the TrailblockAgent
* The TrailblockAgent no longer needs to deal with Edition; the appropriate Trailblock Descriptions now deal with this. Edition is removed from TrailblockAgent

There will need to be a way to do other searches, such as a Tag search or a Content search.