Update TensorImpl constructor to take the tensor  dimensions instead of the number of elements. Necessary for backend_opencv.

- [Syntax] Stimulis -> Stimuli and Stimuli -> Stimulus
- [#define] Use standard Aidge syntax format
- [Licence] add where missing
- [#include] add what is used and remove what is not
- [class] uniformize class member definition order
- [types] change size_t for std::size_t from <stddef> for uniformazation
- [types] change integer types for exact-width integers from <cstddint>
- Remove end-of-line spaces

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