JsonLD: ImageObject, PropertyValue, Url

[nadar]

Add ImageObject, PropertyValue and URL, also change type hinting for those objects.

Due to methods which where not work though implemented, some very small BC problems will appear!

Examples:

• Handling images
• Handling Date / Datetime
• Handling Duration values
• Handling PropertyObjects

We have also added some new types which does not have methods yet, but are important in order to set the correct context type.

Example action for new type hinting:

Argument 1 passed to luya\web\jsonld\BaseThing::setUrl() must be an instance of luya\web\jsonld\UrlValue, string given