Migrate Conversation Pivots module to ApacheSolr AutoTrack and Recommender API.

The Conversation Pivots module is discontinued in favor of Apache Solr AutoTrack and Recommender API. The two modules provides much more powerful features.

TO-DO:
1. Documentation on how to help existing users of Conversation Pivots to migrate to the new modules.
2. Might be better to write an umbrella module that combines the AutoTrack and Recommender modules and provides an easier config interface.