Perform initial cell type comparisons between bulk and single-cell

[sjspielman]

Once we have consensus cell types finalized for single-cell samples in ScPCA, we should perform some initial comparisons between them and estimates from quanTIseq and EPIC. The goal here is not (yet!) to perform a full in-depth comparison, but to help us assess whether it's reasonable to move forward with the current quanTIseq or EPIC results, which are rather different from one another. If one corresponds much more to single-cell cell types, that may help us to choose one over the other depending on consistency with single-cell cell types. If we see that both quanTIseq and EPIC are highly distinct from single-cell inferences entirely, it suggests we might focus more strongly on pursuing our own reference (#126).