[pius-report] Support for storing that someone else won't sign us

[jaymzh]

libpius/state

• Add new version 3 of state file, including new metadata to identify it
• v3 state file includes both 'inbound' and 'outbound' info now
• Add better support for detecting the various versions of the statefile and converting them to v2
• Added unittests
• add debug
• drop all classmethods and ensure people can and do instantiate us

pius

• instantiate SignState(libpius/state)

pius-report

• Add new feature to re-ask about all keys on a keyring
• Add new feature to update state for a specific key
• Add support for new libpius/state features (inbound signing info)
• Tell Signer to sort keys for us

test/libpius/test_state.py

• unittests for statefile conversion