Post types don't load in Gutenberg interface when Gutenberg is installed.

Two things are required on a post type definition to trigger Gutenberg to activate:

* Gutenberg won’t load for a post type that doesn’t support the default editor. If we want to support Gutenberg, we should add support for the editor to all post types in /lib/class-fm-demo-data-structures.php
* Likewise, Gutenberg won't load if the post type isn't available via the REST API. We should add support for REST to all post types in /lib/class-fm-demo-data-structures.php