ADS-B MultiFeeder Suggestion: Support generic adsbexchange base or aggregator

[MaxMyzer]

Since there are several ADSBexchange spin-offs, it might be good to allow users to configure their own feeder upstreams that use the format. I will look into adding it myself if I get a chance.

For a more complete list of adsb feeding sites, adsb.im has a list of supported sites.