Add option to remove other loggers

[304NotModified]

On by Default

.ConfigureLogging((context, logging) =>
{
    // clear all previously registered providers
    logging.ClearProviders();

    // now register everything you *really* want
    // …
});

[snakefoot]

Alternative have option that replaces the current LoggerFactory with the NLog LoggerFactory. Then all other providers will automatically be removed.

It will also have the extra side-effect that only NLog-Logging-Rules has effect, so it is simpler to diagnose (Not being confused by environment-specific appsettings.json files).

[snakefoot]

Resolved by #657 that adds the option ReplaceLoggerFactory (And RemoveLoggerFactoryFilter that will become enabled by default with ver. 5)