Remove all usages of hippostd:document and deprecate the type in HippoStdNodeType#NT_DOCUMENT

The nodetype HippoStdNodeType#NT_DOCUMENT should not be used anymore.
Depreciate it and remove the locations in the unit tests where it's used.

Rationale

• For hippostd:document the hippostd:content field is mandatory. Not all document types have a html field.
• The hippostd:document is very little used any more ( see affected files in the commits )
• hippostd:content as property of hippostd:document is a String field and does not support the ckeditor plugin with links to documents.
• There is no reason the keep a constant for a primary type that is not used anymore.

Backwards compatibility

The hippostd:document type won't be removed from the cnd. Existing documents using hippostd:document are garanteed to function until the latest minor version of 14.x. From 15.0 the type should not be used anymore.

https://code.onehippo.org/search?utf8=%E2%9C%93&snippets=&scope=blobs&search=HippoStdNodeType.NT_DOCUMENT

https://code.onehippo.org/search?utf8=%E2%9C%93&snippets=&scope=blobs&search=hippostd%3Adocument&group_id=518