Support progressive JPEG (Feature #3547)

Hi,

I'm currently using OpenCV in a node.js project which goal is to serve responsive images for the Web: https://github.com/ngryman/ribs/tree/develop.
As you may know, progressive JPEGs have become quite popular (again) those days, and people want to use them on their websites because loading "feels faster" (http://calendar.perfplanet.com/2012/progressive-jpegs-a-new-best-practice/).

Keeping that in mind, it would very nice to add a way to save progressive JPEG.
If I'm not wrong, it would just be a call to jpeg_simple_progression to enable progressive JPEG.

It would involve adding an additional parameter value to cv::imencode and cv::imwrite functions, something like this:

vector<int> params;
params.push_back(CV_IMWRITE_JPEG_PROGRESSIVE);
params.push_back(1);

Do you think this would be something that you could consider?

Thanks!