Add IdentitySafeLogging trait to sanitize logs

This removes sensitive information from the logs.
Add safe logger to other parts of Identity
Update logging in Identity API client now uses safelogger
Add log sanitisers for some sensitive JSON strings
Remove SafeLogger factory method

Encourage people to use SafeLogger as a mixin. This is achieved by
having SafeLogger explitictly replace the Logger found in the client.
Merge pull request #1405 from guardian/clean-identity-log-messages

Unifying ID logging and clean log messages