[backend] create an api endpoint to get the list of videos and share links

[lcfb91]

the reply should be

[
  {
    "title": "<title>",
    "description": "description",
    "link": "<youtube_link>",
    "share": {
          "facebook": "<facebook_video_link>",
          "twitter": "<twitter_video_link>"
    }
  },
  ...
]