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.
added URL logging on failure
Merge branch 'master' of https://github.com/guardian/frontend
added referer based return url detection and fixed a couple of minor issues with signin page
Support external videos
Provide support for a range of external providers
Config for page search size
Merge branch 'master' into fronts-tools-search
Support wikipedia links
Make sure we are requesting actual urls
Paginated search
Merge branch 'master' of github.com:guardian/frontend into external-linked-content-cards
BBC Links
Better messages
Add logging to Futures in parseResponse
Add what was failing to log messages