Search changes

This pull request contains the following:
 - ElasticSearch tests are now enabled when running runtests.py
 - Removed Searchers
 - Removed object_indexed and Indexed.indexed
 - Removed direct dependency to pyelasticsearch
 - Search signal handlers now add/delete to all backends
 - Added subtree search
 - Frontend views now search only the current site (using subtree search)
 - Unified frontend views
 - Frontend views are now configured in urls.py
 - Removed search_name