Individual markers: remove the "one file per marker" checks.
Individual markers: remove the "one file per marker" checks. As Stéphanie as change the way she generates the "individual marker files" (she now sometimes puts more than one marker in the file), the code has to be adapted. In particular:
- no checks that there is one file per marker.
- take all input files (whatever number there is), and extract and merge the "Phenotype" column.
- For the marker intensity data, the values are the same across all files (or should be), so we can just take the values from any file and maybe check that they are equal to the other values.
Overall this should simplify things a bit.