Stop requiring CConnection::serverInit() to be overridden

Add an explicit callback for subclasses to do their startup in. This
makes it easier to do proper ordering, and avoids mistakes.
diff --git a/vncviewer/CConn.h b/vncviewer/CConn.h
index 5988a94..66ef1d0 100644
--- a/vncviewer/CConn.h
+++ b/vncviewer/CConn.h
@@ -51,7 +51,7 @@
   static void socketEvent(FL_SOCKET fd, void *data);
 
   // CConnection callback methods
-  void serverInit();
+  void initDone();
 
   void setDesktopSize(int w, int h);
   void setExtendedDesktopSize(unsigned reason, unsigned result,