Tagging as types

[Cypher1]

Current State

Data types and tags are currently modeled as two separate (but parallel) properties of nodes.
This will make the implementation of #41 more complicated as tags are not able to be tracked inside a nested data type.

Future work

Unify the modeling of types and tags along with handling taint from accessible but tagged fields of types.
e.g.

Struct { secret: String & Tagged('private'), name: String }

should taint the same as String & Tagged('private').

[Cypher1]

This should be useful for ArcsJs (added label)