Implement the "inline" account switch button

Make the account switch listview into a widget

src/widgets/accountswitchwidget.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <QListWidget>
+
+namespace chatterino {
+namespace widgets {
+
+class AccountSwitchWidget : public QListWidget
+{
+    Q_OBJECT
+
+public:
+    explicit AccountSwitchWidget(QWidget *parent = nullptr);
+
+    void refresh();
+
+private:
+    void refreshSelection();
+};
+
+}  // namespace widgets
+}  // namespace chatterino