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 =)
fix 500 on bad thread id input
Support disabling push notifications

If the notify server config value isn't present, just don't try to send
push notifications. Reduces logspam errors.
fix missing HTTPNotFound import
add notice per Apache License 2.0 section 4b
Merge pull request #111 from eve-val/disable-live-update

Support disabling push notifications
Merge pull request #112 from eve-val/fix-missing-import

fix missing HTTPNotFound import
Merge pull request #110 from eve-val/fix-bad-id-500

fix 500 on bad thread id input
Merge pull request #108 from eve-val/search

use Solr for search
Merge branch 'develop' into deploy