Add optional support for different filetypes

[0phoff]

There are various different types of files that allow animations in websites (lottie, rive).
It would be nice to add support for these files in this plugin.

A few minimal requirements for adding these formats:

• Support for these formats should be opt-in, so that a user that doesn't need it does not pull in more code and libraries.
• The formats we add, need at least to have a JavaScript API that allows to start and stop the animation in question. If not, it is not possible to control them...

[0phoff]

Issue #3 should be resolved before we tackle this one !