Adding LabelGeometryImageFilter as a dual image filter

Change-Id: I13abbca1817c4a58707ff1c828211388476eebd6
Add GetNumberOfLabels and HasLabels as custom methods

Change-Id: I0758602a5157f0ca53adb306e94b8442ac1d346b
Merge topic 'SIMPLEITK-524_AddLabelGeometryImageFilter' into next

2776ac76 Add GetNumberOfLabels and HasLabels as custom methods
cbb4e97b Adding LabelGeometryImageFilter as a dual image filter