Normalize the count data within each modality. The default
normalization, which should be used when using the KL divergence, is median
library size normalization Zheng2017,Elyanow2020jrSiCKLSNMF. To perform median library size normalization,
each count within a cell is divided by its library size (i.e. the counts within a column are divided by the
column sum). Then, all values are multiplied by the median library size
(i.e. the median column sum). To use the Frobenius norm, set frob=TRUE to log\((x+1)\)
normalize your count data and use a desired scaleFactor.
You may also use a different form of normalization and store these results
in the normalized.count.matrices slot.