Windows client UX improvements: Change servers while active, start Service when needed

[e-t-l]

A few small things that would make Amnezia much easier to use on Windows:

1. Switch the connection to a different VPN server in the server list simply by clicking on it. Currently, clicking on a different server returns the error message: "Unable to change server while there is an active connection," so you first have to disconnect the current server, then select a different server, then click Connect. (In addition to this being a cumbersome process, it also allows for data leaks, because the Killswitch (if enabled) would deactivate when the first server disconnects!)
2. If the "AmneziaVPN-service" is not running for whatever reason, then clicking the Connect button throws an error that the service is not running. It would be better if the client simply started the service and then connected.