migrate to psyplot plugin template
as we did for the other templates (see psy-simple!35 (merged) for instance) this MR finally migrates psy-reg to the psyplot-plugin-template and makes it compatible with psyplot>=1.5.0
as we did for the other templates (see psy-simple!35 (merged) for instance) this MR finally migrates psy-reg to the psyplot-plugin-template and makes it compatible with psyplot>=1.5.0