Fix default string values with floats for float types

Summary:

String default are used in place of float for float types for plotters.

This affects the implementation of the "Plotter Editor" especially at the creation of the spinboxes that checks strictly for the correct type

Relevant isse(s) fixed:

Fixes #15 (closed) (closed)

Part of beat.editor#181 (closed)

Part of beat.tutorial.prefix!1 (merged)