Handle SIGTERM and Ctrl+C (SIGINT) gracefully (#144)

This makes sure that the landing page container exits with exit code 0.
This avoids Watchdog error messages in the Supervisor logs.

While at it, also handle and log errors in case http.ListenAndServe
fails.

main.go

@@ -5,6 +5,8 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"os/signal"
+	"syscall"
 	"text/template"
 	"time"
 
@@ -60,6 +62,23 @@ func main() {
 	http.Handle("/static/Roboto-Regular.woff2", staticFiles)
 
 
-	log.Print("Start webserver on http://0.0.0.0:80")
-	http.ListenAndServe(":80", nil)
+	// Run webserver
+	go func() {
+		log.Print("Start webserver on http://0.0.0.0:80")
+		if err := http.ListenAndServe(":80", nil); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	signalChannel := make(chan os.Signal, 2)
+	signal.Notify(signalChannel, os.Interrupt, syscall.SIGTERM)
+	for {
+		sig := <-signalChannel
+		switch sig {
+		case os.Interrupt:
+			return
+		case syscall.SIGTERM:
+			return
+		}
+	}
 }