fix IOS skippable ads fullscreen toggle

[mysuf]

Now, it behaves exactly how https://developers.google.com/interactive-media-ads/docs/sdks/html5/skippable-ads describes. It forces content player to enter/exit fullscreen which break fullscreen implementation on mobile IOS. The solution will be probably not supporting tech's fullscreen on IOS and to force full window instead.

The question is how it should work when content player is already in fullscreen - programatically exited fullscreen and switch to full window could lead to blinking and bad user experience...

[mysuf]

One solution is adding browser-manager plugin to ima player. When iOS detected, it would add playsinline attribute to tech element and override content player's enter/exit fullscreen methods by passing enter/exit fullWindow methods instead.