Add a "BasePopup" class, which helps add default functionality to any popups (like the search popup)

src/widgets/BasePopup.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "common/FlagsEnum.hpp"
+#include "widgets/BaseWindow.hpp"
+
+namespace chatterino {
+
+class BasePopup : public BaseWindow
+{
+public:
+    explicit BasePopup(FlagsEnum<BaseWindow::Flags> flags_ = None,
+                       QWidget *parent = nullptr);
+
+    virtual ~BasePopup() = default;
+
+protected:
+    void keyPressEvent(QKeyEvent *e) override;
+};
+
+}  // namespace chatterino