Add error pages to Identity

Identity doesn't currently have a webserver in its stack so we're
leakign Play messages to clients. We'll review the stack but in the
meantime this provides standard Guardian error pages on production,
tweaked so they work over https.
Replace deprecated event handlers with loggers
Add OpenGraph image to Content model
Tweak GraphicksMagick command
Use element-assets in the picture cleaner
Merge pull request #1779 from guardian/event-handler-logger

Replace deprecated event handlers with loggers
Merge branch 'master' of github.com:guardian/frontend into content-images-clean
jshint fix
add standfirst to half-card if no image
don't show headline if empty string
adding image profiles and js to load in images
Move terms and privacy policy links on Registration and Sign in pages
Merge pull request #1792 from guardian/fronts-images

Fronts images
spacing tweaks
Merge pull request #1795 from guardian/identity-registration-policy

Move terms and privacy policy links on Registration and Sign in pages
adding baseline to title min-height
Merge pull request #1797 from guardian/fronts-spacing-shizzle

Fronts spacing tweaks
Articles which have a video element should show a main video
Update Element and PictureCleaner tests
Add video poster