add per-room user model

src/UsersModel.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <QAbstractListModel>
+
+class RoomMember;
+
+class UsersModel : public QAbstractListModel
+{
+public:
+        enum Roles
+        {
+                Avatar = Qt::UserRole // QImage avatar
+        };
+
+        UsersModel(const std::string &roomId, QObject *parent = nullptr);
+        int rowCount(const QModelIndex &parent = QModelIndex()) const override
+        {
+                return (parent == QModelIndex()) ? roomMembers_.size() : 0;
+        }
+        QVariant data(const QModelIndex &index, int role) const override;
+
+private:
+        std::vector<RoomMember> roomMembers_;
+};