Prioritise Flash player over HTML5 player for videos.

This is behind a switch.

Older versions of browsers are struggling with the HTML5 player. A simple test has shown this can solve some of our problems, so testing it out.
Merge branch 'master' of github.com:guardian/frontend into prioritise-flash
Fixed merge issue, not to be deleted yet
That should be off by default
Clean up extra line
Video embeds now share player priority
Video embeds now share player priority
Don't add 'vpaid' to the wrong array
Merge pull request #7497 from guardian/prioritise-flash

Prioritise Flash player over HTML5 player for videos.