Add optional "license" and "license_url" parameter

[ioppermann]

Provided information about media might require that some kind of license for that content is shown on the embedding page. Such license information is currently missing.

Example:

{
   "version": "1.0",
   "type": "video",
   "license": "CC BY 4.0",
   "license_url": "http://creativecommons.org/licenses/by/4.0/",
   ...
}

[iamcal]

great idea!

[CanRau]

Flicker already adds license & license_id example

[legendarioLegendario]

{
"version": "1.0",
"type": "video",
"license": "CC BY 4.0",
"license_url": "http://creativecommons.org/licenses/by/4.0/",
...
}

[legendarioLegendario]

{
"version": "1.0",
"type": "video",
"license": "CC BY 4.0",
"license_url": "http://creativecommons.org/licenses/by/4.0/",
...
}