Add two augmentation functions: rotate and light change and more loss weights

[qizhen816]

1. Bounding box and polygon/mask rotate

• Using OpenCV getRotationMatrix2D to get rotaton matrix from the angle given by config files.
• Bounding box points are calculated as well as polygon instance points.
• before:
• after(-20 degree):

2. Image vertical/horizontal linear light change

• Given a linear light interval limit L, then the image light will be linearly adjusted within [-L, L].
• The function is separated to work vertically or horizontally.
• before:
• after(L=100, vertical):
• after(L=100, horizontal):

3. More Loss weight: MASK_LOSS_WEIGHT BOX_LOSS_WEIGHT CLASSIFICATION_LOSS_WEIGHT and MASKIOU_LOSS_WEIGHT

• All 4 kinds of loss weights can be altered in \maskrcnn_benchmark\config\defaults.py