Add Quant Analyzer & YoLov6 Demo

[RachelXu7]

Quant Analyzer provides:

1. compute the sensitivity of the model by quantizing layer by layer; (sensitivity is expressed as model accuracy for now)
2. rank the sensitivity which can show which layer is not suitable for quantization
3. plot the histogram of tensors; (you can choose the number of tensors you want to visualize)
4. automatically load and save checkpoint since there may be too many layers to be analyzed and it will be sad if the program breaks off