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

src/widgets/BasePopup.cpp

@@ -0,0 +1,21 @@
+#include "widgets/BasePopup.hpp"
+
+namespace chatterino {
+
+BasePopup::BasePopup(FlagsEnum<Flags> _flags, QWidget *parent)
+    : BaseWindow(std::move(_flags), parent)
+{
+}
+
+void BasePopup::keyPressEvent(QKeyEvent *e)
+{
+    if (e->key() == Qt::Key_Escape)
+    {
+        this->close();
+        return;
+    }
+
+    BaseWindow::keyPressEvent(e);
+}
+
+}  // namespace chatterino