Increase the number of unit-tests for Tensor

See merge request !89

Support for recurrent networks

See merge request !77

- remove unused code in comments in ArrayHelpers.hpp
- use std::unique_ptr<[]> instead of C style array in Test_Tensor
- use AIDGE_THROW_OR_ABORT as a default implem for zeros() member function

- [#include] Remove duplicated includes, add includes
- [attributes] add default values for mDataType, mImpl and mGrad
- [constructors] Order constructors, change array copy assignment to remove code duplication
- calling grad() does not instanciate the gradient anymore, a dedicated function should do it
- move getAvailableBackends() and operator=(const Tensor&) to cpp file
- Tensor::resize() now handles scalar Tensors

Add tests for nearly evry member function of Tensor (except makeContiguous(), toString() and empty())

Merge branch 'improve_tensor_coverage' of gitlab.eclipse.org:eclipse/aidge/aidge_core into improve_tensor_coverage

- [Add] ``zeros()`` member function to set implpementation elements to 0
- [unit_tests][NF] Add many more cases in Test_TensorImpl.cpp
- [include] update includes in Tensor.hpp

- [Add] ``zeros()`` member function to set implpementation elements to 0
- [unit_tests][NF] Add many more cases in Test_TensorImpl.cpp
- [include] update includes in Tensor.hpp

Resolve "Cannot get attribute of Reshape_Op in Python"

See merge request !81