Remove core of nomensa media player

The media player has been updated and will now be hosted in static. As
such removing it from whitehall repo.
Merge pull request #171 from alphagov/media-player

Remove core of nomensa media player
bump plek
Upgrade Slimmer Gem to get fixed video test helper

Recently the video player Javascript moved into the static repository -
but as the test helpers weren't updated to include it Whitehall tests
started failing as soon as it was removed from the Whitehall repo.

Now that the test helpers are updated, the tests should magically start
passing again.
Make dump script runnable in development
Use nomensa player from the toolkit
Default news image for Scotland Office

[Fixes #43469135]