md5 support in samplesheets

so we can send md5 hashes to galaxy along w urls for input data. right now in the de stepper we support this in the samplesheet upload in a limited way. for the two expected forward/reverse files, we can also include and autodetect columns in the samplesheet for their md5 checksums.. except they have to be called something like md5_1, md5_2 rather specifically.

1. do we want to auto-detect, or include md5 cols in the ui as a choice when classifying columns?
2. if we do auto-detect, is there a more robust way we can do it?