rename init/inference_segmentor to init/inference_model

.dev/benchmark_inference.py

demo/MMSegmentation_Tutorial.ipynb

demo/image_demo.py

demo/inference_demo.ipynb

demo/video_demo.py

docs/en/get_started.md

docs/zh_cn/get_started.md

mmseg/apis/__init__.py

mmseg/apis/inference.py

tools/print_config.py

tools/torchserve/mmseg_handler.py

tools/torchserve/test_torchserve.py