Merge branch 'aggressive-polling' into 'master'

Try harder to connect to contacts

* When an outgoing connection is lost, try to reconnect to the contact straight away
* Use periodic polling for Tor, regardless of whether our hidden service descriptor has been published
* Reduce polling intervals for all plugins (this can be reverted if we solve the connectivity issues)

Closes #262, #314. Hopefully helps with #361.

See merge request !177