AB test opening external links in a new window
Users not in test should open links in same window
Merge branch 'master' of github.com:guardian/frontend into external-links-new-window

Conflicts:
	common/app/assets/javascripts/modules/experiments/ab.js
	common/app/conf/switches.scala
	common/app/views/support/package.scala
Adjust audience of ab test
Use $ instead of querySelectorAll
Merge pull request #3715 from guardian/external-links-new-window

AB test: external links open in a new window