Automatically add blank images for missing tiles

[sophiamaedler]

When imaging on the opera phenix sometimes a tile is missing when the device can't find the focus. This prevents stitching from the rest of the image.

We need to implement a feature which checks if all expected images are present and if not generates a black tiff for the missing files so that the rest of the slide can be stitched.

[sophiamaedler]

first implementation of this in the development branch. Still seems to have some issues which needs to be benchmarked and tested across more datasets.

[sophiamaedler]

implemented in phenix parser automatically. Seems to be functional in all test cases so far.