[Bug] Solve memory leak induced by circular reference using shared_ptr between Node/Node and Node/GRaphView"

- Children Nodes are referenced by weak_ptr in Node
- GraphViews are referenced by weak_ptr in Node

[Merge] GraphView.hpp
[Doc] update documentation for Node.hpp and GraphView.hpp
[Upd] IOIndex_t from signed<uint16_t> to uint6_t. IONb_t is replaced by IOIndex_t because both types represent the same thing.
[Upd] Make many member-function arguments const for Node and GraphView to improve safety