Improve ImageToDBRegistration outputs

This issue gathers several modifications that can help users to understand how the algorithm works.

• returns the transformation as float values : the application could provide two outputs (transformation_x, transformation_y)
• display the nb of points used to estimate translation : in the final loop, we could display how many triplets are taken into account to find a translation
• stops algorithm if all segments have been filtered. Sometimes it happens that no segment is kept. In such case, we need to stop the application instead of returning a [0,0] transform.