[product_extended_segmentation] Messages log related issues when cost doesn't get updated

Created by: osvalr

Task 4989

Required changes

It is required make a couple of changes:

When update cost in standard_price isn't applied but segments, it's needed to write the log message on product.product instead of product.template, this happens in here as showed below:

current code:

...
tmpl_obj.message_post(cr, uid, [product_tmpl_id.id],
                                  'Not Updated Cost, But Segments only.',
                                  'I cowardly did not update Standard new \n'
                                  'price less than old price \n'
...

Include in message log (written in product) the threshold that is based on price delta ( computed_th )