Stream+Search (rebased for multiframe)

Feature description here: https://docs.google.com/a/hypothes.is/document/d/1zW7jKC8pRuBSDmDK-pZeUZi0e-7T9NrwErthYKpJb0I/edit

This is the rebased version for the latest develop branch + the uri search field is working too.

The old user- and tagstream pages are removed, also the old streamer demo page was deleted.
It embodies annotator-store changes too (check: https://github.com/hypothesis/annotator-store/pull/8 )

**Warning!** This PR changes the ES index so reindexing is needed, **careful** with pushing this to prod.