Piano: Create controller widgets for processor parameters

These widgets attach to a processor parameter and keep the two sides in
sync. They will become very useful for smart processor interfaces.

Userland/Applications/Piano/ProcessorParameterWidget/WidgetWithLabel.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/RefPtr.h>
+#include <LibGUI/Label.h>
+
+class WidgetWithLabel {
+public:
+    WidgetWithLabel(RefPtr<GUI::Label> value_label)
+        : m_value_label(move(value_label))
+    {
+    }
+    RefPtr<GUI::Label> value_label() { return m_value_label; }
+
+protected:
+    RefPtr<GUI::Label> m_value_label;
+};