Pull request: all: imp code, err handling

Closes #2571.

Squashed commit of the following:

commit a5b50ee011a995f4ab3d93314acd6f0ca82d99cf
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Mar 15 14:05:25 2021 +0300

    all: imp code

commit bc610f8f438549e8c6b04c8a213b5422dda2aff5
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Mar 12 20:00:14 2021 +0300

    all: imp code, err handling

internal/home/service.go

@@ -236,7 +236,7 @@ func handleServiceInstallCommand(s service.Service) {
 AdGuard Home is successfully installed and will automatically start on boot.
 There are a few more things that must be configured before you can use it.
 Click on the link below and follow the Installation Wizard steps to finish setup.`)
-		printHTTPAddresses("http")
+		printHTTPAddresses(schemeHTTP)
 	}
 }