Audio offset is integer based in configuration, so let's make sure not
to show that there's an applicable offset when the value difference is
too low.
I've also fixed rounding to match expectations (`AudioOffset` is
precision limited to integer), and handled the case where a user adjusts
the slider but also has a suggested offset – previously it would not
enable the button after slider adjustments but now it will work as
expected.
I keep getting feedback that the old design looked like anything *but* a
button to revert defaults. Including people clicking it expecting
opposite behaviour.
This is intended to be a temporary design until we get the full new UI
components online (where this is moved to the right-hand-side).