Kate Middleton, also known as the Princess of Wales, continues to make progress in her recovery following a planned abdominal surgery, RadarOnline.com has learned. The surgery was deemed successful, and she has been discharged from the London Clinic, where she spent nearly two weeks. In a clear sign of her improving health, Kate was able to join her husband, Prince William, and their three children as they set off Friday morning for a “half-term holiday” on the Sandringham estate in Norfolk, where King Charles is currently convalescing as he begins his schedule of regular cancer treatments. “C…