Work in progress: update Django and Haystack

Hi - this isn't a complete pull request, but I hope you can help get it the last mile.

DocuDig uses an old version of Django and a no-longer-available branch of Haystack which was at https://github.com/localbase/django-haystack

I'm trying to update it to work with current versions of Django, Haystack, and Solr. There are three main issues, all with how Haystack talks to Solr
- Haystack is making a schema.xml without custom fields and only has id. I think this is a search_indexes.py issue - https://django-haystack.readthedocs.org/en/latest/migration_from_1_to_2.html#indexes
- Haystack is making schema.xml with references stopwords.txt and stopwords_en.txt, which I've been changing by hand to lang/stopwords_en.txt
- I don't see any data going into Solr, but it's likely because the schema.xml doesn't match (this is the error that I get when I use PySolr directly)

If I can get this running, I'm going to try to get it so that someone could use version control like git or dat to update the data.