This change adds graph data structures Token, Node, Edge and Graph for holding code semantics in the Storage and fills
them with the parsed data. Things to note:
* Token is the base for the classes Edge and Node and holds a unique id.
* Graph is the owner of all Nodes and Edges.
* A Node saves the Edges it is endpoint of.
* An Edge saves the Nodes that are endpoints.
* Nodes and Edges are not subclassed. The different Node and Edge types are distinguished by the enums NodeType and
EdgeType. Type specific fields are therefore available for all types, a check when assigning them prohibits faulty
usage.
* Storage uses the Graph::getNodeHierarchy method, which is not strict about knowing type names beforehand. E.g. if A::B
is passed in and A doesn't exist so far, then node A gets created as NODE_UNDEFINED with B as it's child.
* The Graph methods addNodeAsPlainCopy and addEdgeAsPlainCopy can be used to create a sub-graph without reference to the
original, but with the same ids.
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