Refactoring Tensor

Adding context to Tensor
Adding "active area" to Tensor
Forward declaring TensorImpl in Tensor instead of the another way around
CPU storage is unsigned char instead of void *
todo: memory location for device different than CPU
todo: a Tensor can share a TensorImpl with another Tensor
TensorImpl = storage
Tensor = view on storage

Notes:

• Tensor::getImpl() returns a reference not a pointer, thus client code must replace getImpl()-> by getImpl().
• Tensor.hpp does not includes backend\TensorImpl.hpp but backend\TensorImpl.hpp includes Tensor.hpp. Thus client code needs to include backend\TensorImpl.hpp (with or without Tensor.hpp)

include/aidge/backend/TensorImpl.hpp

@@ -158,7 +158,7 @@ class TensorImpl
         {
             assert(
                 ((coordIdx[i] - mvFirstDataCoordinates[i]) < mvDimensions[i])
-                && (coordIdx[i] > mvFirstDataCoordinates[i])
+                && (coordIdx[i] >= mvFirstDataCoordinates[i])
                 && "Coordinates dimensions does not fit the dimensions of the tensor");
             flatIdx += (coordIdx[i] * mvLayout[i]);
         }