Add explicit threaded=true for werkzeug's engine

When using the internal http engine, make sure Werkzeug gets threaded=true
passed to it by Flask.
Make sure all fp joins are w/ latest statentries

(The previously committed onionoo_api.py already features proper
fingerprint.sid updates when doing import; but we had done some
manual bulk fp table updates before our latest model and import
mechanism implementation; those updates did not make sure fp.sid
is updated to point to latest statusentry.id, making subsequent
JOINs sometimes improper (would report not the latest addresses
and so on.) This was a subtle bug in the overall update procedure.)