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/CMakeLists.txt

@@ -164,6 +164,10 @@ else()
 	set(DOLPHIN_EXE ${DOLPHIN_EXE_BASE}-nogui)
 endif()
 
+if(USE_UPNP)
+  set(LIBS  ${LIBS} miniupnpc)
+endif()
+
 if(ANDROID)
 	add_library(${DOLPHIN_EXE} SHARED ${SRCS})
 	target_link_libraries(${DOLPHIN_EXE}