thymus: the MHC class II arm lands -- 1,488 I-Ab thymic ligands

thymus + ligandome: the NOD tissue labels, settled by measurement

expression: GTEx has no thymus, so add the HPA consensus arm

expression: the mouse normal-tissue reference, and the thymus slice of it

thymus + ligandome: the mouse side, from deposits that needed no reprocessing

SOURCES.md for every tracked directory, and drop the column nobody could define