This introduces an addendum to the Terminal Settings Model spec that
covers inheritance and fallback. Basically, settings objects will now
have a reference to a parent object. If the settings object does not
have a setting defined, it will ask its parent to resolve the value. A
parent is set using the `Clone()` function. `Copy()` is used to copy the
value and structure of the settings model, whereas `Clone()` is used to
copy a reference to the settings model and build an inheritance tree.
## References
#6904 - Terminal Settings Model Spec
#1564 - Settings UI
