Native ANT+ part 2 - USB2 Support and minor improvements

This patch adds support for the Garmin USB2 stick using
libusb-win library. Instructions are included in gcconfig.pri.in
for configuring and installing the neccessary libs.

To enable support for USB1 and USB2 support in the same binary
stubs are created when UsbXpress/Libusb are not available and the
device i/o attempts to use USB2 before falling back to USB1.

Since I was also in the middle of some coding changes I merged
my developments (Mark) with Darren's patch whilst fixing it up
for commit, namely:

1. the configuration screen no longer demands a COMx port
   when using Native ANT+ on Windows.
2.  new signals in ANTChannel notify the ANT class when info is
   stale or lost (but they are not used at present).
3. The previous debug messages have been removed, although new
   debug messages are added for stale/drop/timeout signals.

src/DeviceTypes.cpp

@@ -28,11 +28,15 @@
 
 static DeviceType SupportedDevices[] =
 {
-      { DEV_CT,       DEV_SERIAL,  (char *) "Computrainer",          true,    false },
-      { DEV_ANTPLUS,  DEV_QUARQ,   (char *) "ANT+ via Quarqd",       true,    false },
+#ifdef Q_OS_WIN32
+      { DEV_ANTLOCAL, DEV_USB,     (char *) "Native ANT+",           true,    false },
+#else
       { DEV_ANTLOCAL, DEV_SERIAL,  (char *) "Native ANT+",           true,    false },
+#endif
+      { DEV_CT,       DEV_SERIAL,  (char *) "Computrainer",          true,    false },
       { DEV_GSERVER,  DEV_TCP,     (char *) "Golden Cheetah Server", false,   false },
       { DEV_NULL,     DEV_TCP,     (char *) "Null device (testing)", false,   false },
+      { DEV_ANTPLUS,  DEV_QUARQ,   (char *) "ANT+ via Quarqd",       true,    false },
 //    { DEV_PT,       DEV_SERIAL,  (char *) "Powertap Head Unit",    false,   true  },
 //    { DEV_SRM,      DEV_SERIAL,  (char *) "SRM PowerControl V/VI", false,   true  },
 //    { DEV_GCLIENT,  DEV_TCP,     (char *) "Golden Cheetah Client", false,   false },