Added meta tag to upsell iPhone app

It is behind a switch (off by default)

Will be a simple matter to enable it and then see if we get higher registrations.

Only on UK edition (US has different app)
Added meta tag to upsell iPhone app

It is behind a switch (off by default)

Will be a simple matter to enable it and then see if we get higher registrations.

Only on UK edition (US has different app)
Merge branch 'master' of github.com:guardian/frontend into app

Conflicts:
	common/app/conf/switches.scala
Merge pull request #1088 from guardian/app

Added meta tag to upsell iPhone app