Add basic application framework and example application to show interaction between events an NBI

Depends on:

• !340 (merged)
• !344 (merged)
• !349 (merged)
• !342 (merged)

application-framework/registration/registration.go

+package registration
+
+import (
+	"context"
+	"time"
+
+	"code.fbi.h-da.de/danet/gosdn/api/go/gosdn/app"
+	"google.golang.org/grpc"
+)
+
+// Register registers a new app at the control plane.
+func Register(name, token string) (string, error) {
+	conn, err := grpc.Dial("localhost:55055", grpc.WithInsecure())
+	if err != nil {
+		return "", err
+	}
+
+	ctx := context.Background()
+	appService := app.NewAppServiceClient(conn)
+
+	request := &app.AppRegisterRequest{
+		Timestamp: time.Now().UnixNano(),
+		Appname:   name,
+		Token:     token,
+	}
+
+	response, err := appService.Register(ctx, request)
+	if err != nil {
+		return "", err
+	}
+
+	return response.Queueconnection, nil
+}