Use mapping list of channels for `path_report`

[d33bs]

This looks great! I have another idea for this that I think will be important in the context of the work done in the lab. It is very likely out-of-scope for this PR.

I think there is one other function that will be helpful:

1. Require a mapping or list of the channel names that can be found in the files. From that list, make sure there are the same number of files per channel for that well/FOV. This work will be best for those situations where each folder is a well and the FOV. It is important that there is an equal number of files per channel, as if not, it will cause an error in CellProfiler, and the error in CellProfiler is not intuitive to tell you which z-slice from a specific channel is missing.

Originally posted by @jenna-tomkinson in #42 (comment)