The `BigRedButton` should be a real struct and component so that I can
query for it later.
I'm following the same API pattern as the `CloseButton` struct, in that
there is a spawner using the `Commands` (or `ChildSpawnerCommands`) and
the observer functions are static methods.
That was much easier than I expected it to be. I'm still going to alter
how the `machine_ui_base` function works so that I don't have to
remember to attach a button all the time.
