Add more features in plot module of opencv

[themechanicalcoder]

It would be nice if OpenCV plot can have features similar to matplotlib

1. xlabel, ylabel
2. legends
3. allow plotting of two functions (The current implementation supports only one)
4. A SetTitle function

[themechanicalcoder]

@alalek can I implement some of these functions like SetTitle xlabel, ylabel

[wpalfi]

Hi, I am the developer of Profactor CvPlot https://github.com/Profactor/cv-plot. It is purely opencv based and very generic. Would be great to integrate it into opencv_contrib. What do you think?