Port RT badxixels code to librtprocess

[heckflosse]

I would like to port some of the RT badpixels code to librtprocess to handle bad pixels processing in HdrMerge. Any objections?

[CarVac]

No objections.

What exactly does it do?

[heckflosse]

It has some routines to easily fix bad pixels. Here's an example file:
P1000009.zip
Open it in Filmulator, zoom in and you will see a lot of black pixels (Panasonic sets dead pixels to zero)

And here's the link to the code I want to port to librtprocess:
https://github.com/Beep6581/RawTherapee/blob/badpixels-compunit/rtengine/badpixels.cc