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 =)
Heads-up here that pysolr wants a recent version of requests, while the yubikey library that core uses wants this old version. If you've been running them out of the same virtualenv, that will no longer work.