- [Add] Attributes: __str__(), __repr__() and dict() methods
- [Add] GraphView: __repr__(), __len__() methods
- [Add] Node: __repr__() method
- [Add] Operator: __repr__() method and attr property
- improve Tensor __str__ method if it is empty
- change DataType to lower case for python

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