Support OEmbed remote url

Problem/Motivation

Media entity types using OEmbed remote URLs do not work in the wysiwyg. A file upload field is shown instead of a URL field.

Steps to reproduce

Try to upload a remote video via the wysiwyg.

Proposed resolution

Check if plugin deriver is OEmbedDeriver and load OEmbedForm.

Remaining tasks

User interface changes

API changes

Data model changes