Make Themable pass the current Theme through applyTheme

This reduces boilerplate code and remove the ThemeManager dependency at Thamable subclasses level.

YACReaderLibrary/comic_vine/scraper_checkbox.h

@@ -11,7 +11,7 @@ public:
     ScraperCheckBox(const QString &text, QWidget *parent = nullptr);
 
 protected:
-    void applyTheme() override;
+    void applyTheme(const Theme &theme) override;
 };
 
 #endif // SCRAPER_CHECKBOX_H