Refactor threads

The focus here is to make threads use the standard message content system rather than having a special implementation.

To achieve this the threadroot content model will now get a thread body component which will visualise the thread model with all the other messages. The latest message in the thread will then just ask for the thread root content model and show that.

Note: in order to stop a cyclical dependency with MessageComponentChooser and new base version has been added which is just missing ThreadBodyComponent and and the main version is now inherited from that with ThreadBodyComponent added.

src/models/threadmodel.h

@@ -91,11 +91,6 @@ public:
 
     QString threadRootId() const;
 
-    /**
-     * @brief The content model for the thread root event.
-     */
-    MessageContentModel *threadRootContentModel() const;
-
     /**
      * @brief Returns a mapping from Role enum values to role names.
      *
@@ -117,10 +112,16 @@ public:
      */
     void fetchMore(const QModelIndex &parent) override;
 
+    /**
+     * @brief Close the link preview at the given index.
+     *
+     * If the given index is not a link preview component, nothing happens.
+     */
+    Q_INVOKABLE void closeLinkPreview(int row);
+
 private:
     QString m_threadRootId;
-
-    std::unique_ptr<MessageContentModel> m_threadRootContentModel;
+    QPointer<MessageContentModel> m_threadRootContentModel;
 
     std::deque<QString> m_events;
     ThreadChatBarModel *m_threadChatBarModel;