Renames matmul.cl to operations.cl
Generalizes the old functions to blas form.

- Definitions are moved to the header file.
- Removes matrix_multiplication_cl() functions. The usage can be replicated through blas_sgemm() with alpha=1 and beta=0.
- Creates blas_sgemm kernel functions, almost as a copy of the matmul one.
- matrix_multiplication() function can no longer be accessed, but the code will be removed when blas_sgemm gets the MPI functionality.
- Removes long unused matrix_print() method.
Cleans matmul function in operations.cl.