video embedding stuff is now completely a part of the content extractor plugin (and not as before partially implemented in the ChronologicalPostListWidget) - can be used as an example for implementing similar things that customize the rendering
added some events for easily hooking into the client side rendering of the notes of the ChronologicalPostListWidget
renamed RichMediaUtils to EmbedMediaUtils because it matches better what this helper does
EmbedMediaUtils JavaScript class is hidden, but default options and URL mappings can be customized
videos are now embedded with 16:9 aspect (as YouTube and Vimeo embed codes suggest)
This PR fixes #63
Changes: