gkeys: Refactor the fetchseed action

Update seed file fetching to include the .sig's
Add gkey option to the seedurls config section to be used for verification of seeds.
Use the Action.verfify() to download the seeds, .sig and use the timestamp files.
Make the '.sig' file extension the first tried (detached sig ext.)
Remove some now dead isurl code.
Modify messages to add key.nick instead of key.name
gkeys/actions.py: verify(), Make it use the configured keydir for verification
gkeys/lib.py: Py3 compatibility changes
gkeys/actions.py: Fix loading of multiple keys in one keydir in installed()
gkeys/actions.py: Add debug option to connector_output definition

Change due to ssl-fetch output change
gkeys/actions.py: Tweak verify() output