Add UPnP support.

Feedback is in logs as suggested by skid_au. The checkbox is still there, but
mostly for people who would like to opt out (unfortunately, I can not be sure
how this feature may behave for some routers - there's a hell of a lot of bad
UPnP implementations.)

The Visual Studio stuff is a little messy, so I apologize if anything is a bit
off. I tested most configurations and it worked.

I also tested CMake on Debian Wheezy, Ubuntu Saucy, and Mac OS X Mountain Lion.
All seemed to be OK.

Source/Core/DolphinWX/Src/NetWindow.h

@@ -48,6 +48,9 @@ private:
 		*m_connect_ip_text;
 
 	wxListBox*		m_game_lbox;
+#ifdef USE_UPNP
+	wxCheckBox*		m_upnp_chk;
+#endif
 
 	const CGameListCtrl* const m_game_list;
 };