Added a base ad name for the features and people containers
Prevent top ad slot from overflowing out of the page
Merge pull request #3174 from guardian/fronts-mpu-fix

Added a base ad name for the features and people containers
Merge pull request #3175 from guardian/hotfix-adslot-over

Prevent top ad slot from overflowing out of the page
'Stretch' in body images to 620 if they are smaller
Merge branch 'master' of github.com:guardian/frontend into picture-this