Implement the "inline" account switch button

Make the account switch listview into a widget

src/widgets/accountswitchpopupwidget.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include "widgets/accountswitchwidget.hpp"
+
+#include <QWidget>
+
+namespace chatterino {
+namespace widgets {
+
+class AccountSwitchPopupWidget : public QWidget
+{
+    Q_OBJECT
+
+public:
+    AccountSwitchPopupWidget(QWidget *parent = nullptr);
+
+    void refresh();
+
+protected:
+    virtual void focusOutEvent(QFocusEvent *event) override final;
+
+private:
+    struct {
+        AccountSwitchWidget *accountSwitchWidget = nullptr;
+    } ui;
+};
+
+}  // namespace widgets
+}  // namespace chatterino