[Room][UserList] Introduce style delegate for user list

- Allow users to set a card name and parameters as their background banner
- Allow mods to white/blacklist cards
- Allow toggling back to the old display style

Took 7 minutes

Took 28 seconds

Took 2 minutes

Took 2 minutes

cockatrice/src/interface/widgets/server/user/user_avatar_provider.h

@@ -0,0 +1,30 @@
+#ifndef COCKATRICE_USER_AVATAR_PROVIDER_H
+#define COCKATRICE_USER_AVATAR_PROVIDER_H
+
+#include <QMap>
+#include <QObject>
+#include <QPixmap>
+#include <QSet>
+
+class AbstractClient;
+
+class UserAvatarProvider : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit UserAvatarProvider(AbstractClient *client, QObject *parent = nullptr);
+
+    void requestAvatar(const QString &userName);
+    const QMap<QString, QPixmap> &cache() const;
+
+signals:
+    void avatarUpdated(const QString &userName);
+
+private:
+    AbstractClient *client;
+    QMap<QString, QPixmap> avatarCache;
+    QSet<QString> pending;
+};
+
+#endif // COCKATRICE_USER_AVATAR_PROVIDER_H