Haystack (search) integration

WIP

* Index events (including speaker's names, tags, department and location)
* Query events (including full-text search, faceting, suggestions)
* Provide schema for Solr

TODO:
* sort out boosting of results (prefer results in the near future)
* sort out date range facet
* index events on save/update/delete
* define what kind of results we want back: (only events or speakers as well for example)
* define what search we need to expose through the API
* define suggester

Yes they are... will need to be discussed but I think it makes sense to refine by these criteria. Might need to be extended to more criteria, I think this code will be moved to a specialised search form anyway.