Indie Web Server 9.1.0: Better error handling

Indie Web Server version 9.1.0 is a minor release that handles the following two, related (and common), errors more gracefully:

1. Trying to enable a web server daemon when one is already enabled

   Previously, this would succeed even though the earlier server would continue to be served. Now, it gives an error and instructs you to disable the existing server.

2. Trying to enable a web server daemon when some other service was using port 443

   Previously, this would succeed but your server would only start running once (and if) the service blocking port 443 exited. Now, it gives an error and exits.

3. Trying to start a regular web server process when some other service is using port 443

   Previously, this would fail but show a stack trace. Now, it shows a friendly error and no longer shows the stack trace.