:dart: Add more configuration options to `qan::Navigable`

[cneben]

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• ~~Add progressive zoom in/out.~~
• ~~Add support for [min, max] zoom.~~
• [X] Add a graph / graphView link.
• [x] Add graphBr concept to qan::GraphView with a valid initial size. graphBr should evolve with container item childrenRect !
• [X] Add scrollbars support.