backend: add Linkbox backend

Add backend for linkbox.io with read and write capabilities

fixes #6960 #6629

backend/linkbox/linkbox_test.go

@@ -0,0 +1,17 @@
+// Test Linkbox filesystem interface
+package linkbox_test
+
+import (
+	"testing"
+
+	"github.com/rclone/rclone/backend/linkbox"
+	"github.com/rclone/rclone/fstest/fstests"
+)
+
+// TestIntegration runs integration tests against the remote
+func TestIntegration(t *testing.T) {
+	fstests.Run(t, &fstests.Opt{
+		RemoteName: "TestLinkbox:",
+		NilObject:  (*linkbox.Object)(nil),
+	})
+}