Adding a stage02 script for signal convolution

[cosimolupo]

Building on recent observations that analog signals derived from spike trains may need to be convolved with some finite-size width analytic function, here we provide a script for a channel-by-channel convolution of the signal. As of now, the unique possibility is a convolution with a Gaussian kernel with customizable parameters, but the block can be easily extended with additional analytic functions. The template config file has been coherently updated.