expand the initEmbed function to allow setting field values

It would be great if the initEmbed could be used to set the field values instead of using url search parameters.

Also to be able to set a class to the body of the embedded document so when using customcode styling can be adjusted. This makes it easier to embed the same form on different background color’s

Bonus if it would be possible to set field values after the embedded form is loaded. Otherwise this would only be possible by resetting the iframe-src.