Add ability to pass additional args to FaceAnalysis constructor such as 'root'

[provinceperformer]

Add ability to pass additional args such as root to FaceAnalysis constructor, so they do not have to put the model files in their home directory

Example:

model = insightface.app.FaceAnalysis(root='./models')
ctx_id = -1
model.prepare(ctx_id=ctx_id, nms=0.4)