Change how room avatars are passed, fix friend avatars not loading

The problem lies in how media URLs work, in this case it the old
NeoChatRoom::avatarMediaId could pass a mxc url *or* a path that can
be put into root.connection.makeMediaUrl. So normal rooms with avatars
loaded, but never friends because room members gave the mxc URL.

Instead, change everything to use avatarMediaUrl which corrects this
issue by always passing a mxc URL to QML. This also removes the need to
call makeMediaUrl.

Fixes #675

(cherry picked from commit 6b79795229)

src/neochatroom.h

@@ -69,9 +69,9 @@ class NeoChatRoom : public Quotient::Room
     Q_PROPERTY(bool readMarkerLoaded READ readMarkerLoaded NOTIFY readMarkerLoadedChanged)
 
     /**
-     * @brief The avatar image to be used for the room.
+     * @brief The avatar image to be used for the room, as a mxc:// URL.
      */
-    Q_PROPERTY(QString avatarMediaId READ avatarMediaId NOTIFY avatarChanged STORED false)
+    Q_PROPERTY(QUrl avatarMediaUrl READ avatarMediaUrl NOTIFY avatarChanged STORED false)
 
     /**
      * @brief Get a RoomMember object for the other person in a direct chat.
@@ -320,7 +320,7 @@ public:
 
     [[nodiscard]] bool readMarkerLoaded() const;
 
-    [[nodiscard]] QString avatarMediaId() const;
+    [[nodiscard]] QUrl avatarMediaUrl() const;
 
     NeochatRoomMember *directChatRemoteMember();