Improve definition references

[adamgerhant]

Improves the definition reference system by referencing nodes with DefinitionIdentifier instead of strings. Sets the foundation for git style node versioning system since a hash and other metadata can be added to each identifier.

For example:
instead of

resolve_document_node_type("Star")

you would do

resolve_document_node_type(&DefinitionIdentifier::ProtoNode(graphene_std::vector::generator_nodes::star::IDENTIFIER))

Another example

resolve_document_node_type("Merge")

to

resolve_document_node_type(&DefinitionIdentifer::Network("Merge".to_string()))

TODO: Fix tooltip showing Object object, skip impl nodes have no name