Override a default config to avoid copying between config files

[maartentamboer]

Many of my plane settings habe common rotary/buttons. Is it possible to have a common config file and only plane specific values in other files (other languages have something like a perform) . I'm not talking about global values.
Yes I understand the problem of aircraft load time, we would have to wait until the flight/plan is really loaded.
thx

Originally posted by @reimuell in #57 (comment)