Add IdentitySafeLogging trait to sanitize logs

This removes sensitive information from the logs.
Add safe logger to other parts of Identity
Removed gallery lighbox ab test
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 in expandables story packages
Merge branch 'expanding-reading-story-packages' of github.com:guardian/frontend into right-hand-story-package
Merge branch 'expanding-reading-story-packages' of github.com:guardian/frontend into right-hand-story-package
added some useful readme comments
Merge branch 'expanding-reading-story-packages' of github.com:guardian/frontend into right-hand-story-package
Added frontend config to the configuration stack
Add view fragments for cards
Merge branch 'master' into frontsFeatures
Added frontend config to the configuration stack
added URL logging on failure
Merge branch 'master' of https://github.com/guardian/frontend
Added recent controller and endpoint to core-nav
added referer based return url detection and fixed a couple of minor issues with signin page
Support external videos