refactor: split formatters and matchers into separated singleton classes (#166)

* split formatter into separated singleton classes

* split data engine matchers to classes

* nodiscard attribute for formatter methods

* small refactoring in matchers

* fix codefactor warnings

* fix test building

sources/desktop-panel/plugin/dpadds.h

@@ -28,7 +28,7 @@ class VirtualDesktopInfo;
 class WindowTasksModel;
 } // namespace TaskManager
 
-class DPAdds : public QObject
+class __attribute__((visibility("default"))) DPAdds : public QObject
 {
     Q_OBJECT