Fix attributes names in cpp tests

The previous behaviour was to keep the Tensor of the removed layer. Now it is also removed

[Fix] (tmp) GraphView::forward_dims() if dimsension provided and Tensor already associated

- [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] attribute() member function of Oeprator. Return nullptr if no attributes
- [Fix] Scaling attributes names from camelCase to PascalCase

Move StaticAttribute from Base class to member attribute

Fix bias

See merge request !141

Fix fuse mulAdd (and more ;))

See merge request !137

Add log operator for BCE loss function

See merge request !140

Multiple fixes

See merge request !139

Alternative graph matching

See merge request !138