Add image adjustment features

[dancleaver]

Might use imgproc-rs or image2.

[dancleaver]

One thing for sure that needs to be added is image adjustments (exposure, levels (combined-RGB input black level, gamma, input white level - like the Levels image adjustment in Photoshop) and white balance selection for tungsten and daylight. Basically, we need post-processing controls to make the final image to look as good as possible

[clostoski]

Mostly done, white balance still needs to be done.

[MickHarrigan]

Addressed in #91 and its predecessors