Made step to remove ASyncWindow in favour of usage of Future and FutureWatcher.

This should allow concurrency in the plugins to be independent from their container.

Contains also some work on the system for registering plugins.

pglab/plugin_support/MenuLocation.h

@@ -0,0 +1,17 @@
+#ifndef MENULOCATION_H
+#define MENULOCATION_H
+
+#include "plugin_support/MenuPath.h"
+
+class MenuLocation {
+public:
+	MenuLocation();
+	MenuLocation(MenuPath path, int position = -1);
+
+	bool isEmpty() const;
+private:
+	MenuPath m_path;
+	int m_position = -1;
+};
+
+#endif // MENULOCATION_H