Redesign how LengthParameter manages default settings in database vs instantiation

[JansenSmith]

Basic goal is to make it either more obvious or more controllable whether instantiating a LengthParameter object is setting a backup value while linking to an existing object or instead is creating a new thing with a starting value set here and now as the provided value.

related to: https://github.com/CommonWealthRobotics/BowlerStudio/issues/315