add unit/integrted tests for dpc

It's not simply generating a list of synthetic images. There are a reference image and associated images for each DPC calculation. The DPC calculation process and underlying theory can be checked in the integrated_test.

If generating a set of random images, I don't know how to analytically compute the final phase image other than running the dpc code to see the final result (@licode do you have any idea). I have verified results (text and JPEG files) from previous C code. I can compare the results with those text and JPEG files.