Use @graph with multiple types on root level

[Chris Müller]

When embedding multiple schema types on the root level of a page, the @graph property can be used. This is considered equal to use an array of types or multiple script tags. The advantage of @graph is, that the context must be used only once, so the JSON-LD string is smaller - especially with many many types on a page.

Acceptance criteria:

• If only one type on root level is available, this type is embedded as previously.
• If more than on type on the root lebel are available, the @graph annotation is used to group them together.
• The documentation is adjusted (if applicable).

Resources:

• https://stackoverflow.com/questions/30505796/json-ld-schema-org-multiple-video-image-page/30506476#30506476
• https://www.w3.org/TR/json-ld/#h3_named-graphs