This PR updates the behavior of the gridsync.wormhole_.Wormhole QObject/wrapper to delay creating the underlying wormhole object (from the magic-wormhole library) until Wormhole.connect() is called. This fixes the situation in which Gridsync/magic-wormhole would needlessly open an idle connection to the relay/rendezvous server during initialization (despite not actually using that connection -- thankfully -- in the event that the user enables Tor).

Fixes #169

Big thanks to @abmoka for noticing this!