Fix compilation of LibjingleCallDialog

This fixes compile error of jabber protocol when libjingle is enabled.

In file included from kopete/protocols/jabber/libjinglecalldialog.cpp:16:0:
kopete/protocols/jabber/libjinglecalldialog.h:28:56: error: invalid use of incomplete type ‘class QDialog’
 class LibjingleCallDialog : public QDialog, public Ui::LibjingleCallDialog
                                                        ^~~~~~~~~~~~~~~~~~~