Support for the new AST in Graph API

[mwu-tow]

Summary

Currently existing parts of double representation efforts (branch mwu/graph-syntax ) has some initial implementation for a few methods that used then-available AST. Now AST has been changed and the branch must be updated.

Value

The new AST will be the only AST — so this is a requirement.

Specification

Merge branch with new AST into graph-syntax branch. Fix all the errors.
The node-processing methods can get commented out. (will use a different approach anyway)

Acceptance Criteria & Test Cases

Import operations are still supported. Branch compiles and passes tests.

[mwu-tow]

Mostly done, only text API parts needs updating. Requesting help from @Josef-Vonasek