Add an option to remove Core themes from Theme Field selector

I dont want my site administrators being confused by random stuff like "Seven", "Classy", and "Stable". I thought maybe I could just disable Classy, but no, it must be enabled because Seven depends on it. My other custom themes depend on "Stable" and it cannot be disabled.

So, this request is to provide a UI (eg a module settings page) to select which enabled themes should be removed from the option list exposed to content creators.

Of course I could do this via a form alter, but this would in theory be a very common feature that many people would want.