Make sure the MessageContentModel starts at UserRole

If it doesn't, then our roles start filling up the other Qt ones such as
AccessibleDescription. Instead we need to start UserRole (except for
DisplayRole of course.)

src/timeline/models/messagecontentmodel.h

@@ -41,7 +41,7 @@ public:
      */
     enum Roles {
         DisplayRole = Qt::DisplayRole, /**< The display text for the message. */
-        ComponentTypeRole, /**< The type of component to visualise the message. */
+        ComponentTypeRole = Qt::UserRole, /**< The type of component to visualise the message. */
         ComponentAttributesRole, /**< The attributes of the component. */
         EventIdRole, /**< The matrix event ID of the event. */
         TimeRole, /**< The timestamp for when the event was sent (as a QDateTime). */