update reindex backround task to current indexing workflow

- Error if MEDIA_BASE doesn't exist.
- Delete and recreate index.
- Add mappings and facets.
update docstore status reporting to work with Elasticsearch 1.0

Elasticsearch changed its status format. This commit adapts to
that and adds a couple new features.
- Alert if no connection to Elasticsearch server.
- Alert if no indices present.
- List size,num_docs for each index.
don't attempt to add URLs to search results placeholder objects

Recap: Django paginator needs to have the entire result set.
We don't want to actually keep the entire set so we keep the
current page and pad the results with placeholder objects.