Delete elasticsearch index on deletion, omit trash search results

[max-zilla]

#377

This does 2 things:

• Files, datasets, collections are removed from Elasticsearch index on deletion.
• Files, datasets and collections are checked for trash status before display in search results. Search is filtered by ID so hopefully quick retrieval. Not sure how else to double-check ES index isn't out-of-sync.

Currently deleting index doesn't happen on trash, only delete - in theory people might want to search trash? But I'm not sold on this so if we think it should be done on moving to trash I can adjust it.