Feature Request: Increase flexibility of to_Seurat

[JohnMMa]

I realized one thing: currently, to_Seurat will always write the expression to the assay of 'RNA'. I wonder if devs may add an option so that we can customize the assay the expression to be written to? We often do pure CITE-seq experiments, which means output from that usage should be in the assay of 'ADT'--which means an entire new Seurat object needs to be created to carry on the assay data because the assays' names of Seurat objects cannot be directly modified.

[rcannood]

#183 tries to address this issue. @JohnMMa Would the proposed changes work for you?