Connect to new contacts

The motivation for this change was realising that when we add a new contact, if the Tor plugin has finished publishing its descriptor and stopped polling, we'll never try to connect to that contact via Tor. I decided that instead of making a special case for Tor, we should try to connect to new contacts via all transports.

Changes:
* Don't register outgoing connections until we've read the incoming tag - this prevents the connection indicator from blinking when connecting to a contact who's removed us
* Connect to newly activated contacts using all available transports, without waiting for the poller
* Removed device IDs from transport properties, we don't know how we're going to handle multi-device support yet


See merge request !135