Backwards - ReLU & Dense Lasyer

Made the backwards for dense layers and ReLU, but I think I soon need to refactor some code to make it all steamlined.

include/utils/matrix.h

@@ -23,7 +23,6 @@ namespace utils{
 	class Matrix{
 public:
 	    Matrix() : rows_(0), cols_(0), data_() {} // Default constructor
-#include <random>
 	   // Constructor to initialize matrix with rows × cols and a fill value
 	    Matrix(uint64_t rows, uint64_t cols, const T& value = T()) 
 	    : rows_(rows), cols_(cols), data_(rows * cols, value) {}