GH-43: started to prototype the python side of the interface

[sanbales]

NOTICE: Not ready for review

Putting this up as PR to elicit input from @nrbgt and @dfreeman06 .

References

Addresses #43

Code changes

• Adding a new NodeShape behavior that allows for using a declarative approach to drawing on the canvas (leverages declarative-canvas library)
• make sure it can be used in 3D as well
• add declarative-canvas to the ts side and implement the interfaces there

User-facing changes

• Allows for users to make the nodes look like circles, rectangles, use images, a custom path, or text.

Backwards-incompatible changes

• None.

[github-actions]

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