Get rid of the service.mode switch

[nigredo-tori]

The existing solution for #35 (service.mode setting) requires passing command-line arguments to disambiguate between running as an application and as a service. This is inconvenient and unnecessary. What we should do instead is to call StartServiceCtrlDispatcher first - and then, if it returns ERROR_FAILED_SERVICE_CONTROLLER_CONNECT, run as a simple application.