Infogram implementation

[KurtTrowbridge]

Hello!

I'm working on a project that uses Infogram for a lot of data reporting within their articles, and needed to be able to auto-convert from their standard embed codes that have been added as Drupal content to their recommendation of amp-iframe elements.

This pull request essentially mimics what @obeyer did for Tumblr and Imgur compatibility. I've tested this and it's working for me, but if you need any more information, please let me know. Thanks!