Thoughts about HOGDescriptor related to OpenCV 5

[sturkmen72]

Detailed description

recently i used cv2.HOGDescriptor() in pyhton and the following ideas came to my mind

1. HOGDescriptor is implemented as struct i think it could be re-implemented as class
   this will solve documentation issues about it ( currently no python usage of methods showed in the documentation).
   also solves the following issue:
   hog = cv2.HOGDescriptor() ( equal to hog = cv2.HOGDescriptor((64, 128), (16, 16), (8, 8), (8, 8), 9)) works.
   hog = cv2.HOGDescriptor((64, 128), (16, 16), (8, 8), (8, 8), 9) works
   hog = cv2.HOGDescriptor((64, 128)) raises an error. ( for giving a new value to one parameter we need give values to other parameters even they have default values )

2. it is possible to drop getDefaultPeopleDetector() and getDaimlerPeopleDetector() functions. we can save their values into files like haarcascade files and hog.load() method is enough to load them.

3. Some of the parameters not used at all in the implementation can be cleaned up.

i can work on this if the ideas in general sound good.

[asmorkalov]

/cc @vpisarev