webui: added check for empty avatars and implemented avatar notify callback

git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@8551 b45a01b8-16f6-495d-af2f-9b41ad6348cc

libresapi/src/api/PeersHandler.h

@@ -20,6 +20,7 @@ public:
     // from NotifyClient
     // note: this may get called from foreign threads
     virtual void notifyListChange(int list, int type); // friends list change
+    virtual void notifyPeerHasNewAvatar(std::string /*peer_id*/);
 
     // from Tickable
     virtual void tick();