Support for "media" tag and possible usage with more then one video version (Responsive video)

[fanningert]

Idea for usage

(videoext [options1])
  (video: {src} [options2])
(/videoext)

• options1 - current kirbytext video options
• options2 - media, type for source element

With this code variant, it is easy to add a video. Simple drag and drop video panel web frontend.