This reverts commit ffc4d22e.

Add a trampoline to Node.add_child in order to set None default value to avoid conversion of nullptr -> std::shared_ptr.

- Remove setInput in Node
- Change setDatatype to setDataType in GraphView and Tensor binding
- Add namespace comment
- Update Node includes
- Run forwardDims() only if operators use Tensors

Changed outputs() and getNbDataInputs() in GraphView to achieve consistent behavior (clarified in doctring)

[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