added IMixedRealityPointerHandler in train.cs for implementing moveTrain function later
added a ghostTrain for visualization in addTrainUI
added some texture images and a ghostTrain prefab
added some comments in scripts for documentation
added a miniMapUI for displaying the current score & week, but the camera is not functioning properly in play mode (the expected behavior is a top-down view camera, but it's showing a front view now...)