use Solr for search

This includes no UI. I have a bad UI I've been using to test with, but
it's not ready for prime-time yet. In the interest of keeping changes
small I thought I'd send this for review =)
pysolr is pretty mediocre. It claims that lxml is an optional requirement, and then if there is a solr error and solr is running on tomcat, it tries to import lxml.html with no fallback, blowing up terribly. So if you want to get good error messages out of solr, it make take some effort.