New "localonly" option for resolvers

[RJ]

Resolvers can now set themselves as "localonly", meaning they will only be asked to resolve queries originating on the machine on which they are running. This means you can load resolvers that search private sources without worrying about people on your network streaming from them.

EG, you might want to set a resolver to localonly if you have to pay for content it matches, or if the source it resolves against only allows one connection at a time. (Rhapsody/spotify/whatever).

Also, if you're developing a resolver that isn't yet ready, mark it as localonly to avoid others on your network triggering it.

Plugins can implement bool localonly() const { return true; }
Scripts can add "localonly":true to the settings object they return

As usually, you can override settings declared by the resolvers in the config file.