REL-1501: Storing Scale Interpolation in TPE and code cleanup.

This is just a quibble given that the entire thing is private and the class is tiny.  Still we could separate the loading of the preference and turning it into a `ScaleInterpolation` from the side effect of updating the menu selection.  On the other hand I guess this is never going to be pure function anyway given that it reads from mutable source (`Preferences`), but it still might be an improvement.  Regardless, we should log the exception instead of just printing it there so it shows up in the log.  Since it isn't critical it could just be at `INFO` priority I guess.