maximum memory usage too high in resolve_conflicts.py

[aryarm]

In resolve_conflicts.py we load the entire orthomosaic into memory just so that we can get its dimensions. This is probably very memory inefficient.
There are a couple of potential solutions:

1. Save the image dimensions in the segments file during the segmentation step, so that resolve_conflicts.py can just load it from there
2. Use a python library that can get the image dimensions without loading the file into memory (unlike PIL)