Standardize markers.csv

[ArtemSokolov]

Adjust the exemplar markers.csv and the corresponding code to conform to the agreed-upon format. Example, as provided by @clarenceyapp:

channel_number,cycle_number,marker_name,Filter,excitation_wavelength,emission_wavelength
1,1,DNA,DAPI,395,431
2,1,A488_background,FITC,485,525
3,1,A555_background,Sytox,555,590
4,1,A647_background,Cy5,640,690

Note that channel names cannot have spaces or dashes, as required by the downstream HistoCat module.