Problem using factor to index matrix

* master:
  Fix group factors bug

From: Luke Zappia <lazappi@users.noreply.github.com>

git-svn-id: file:///home/git/hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/splatter@131740 bc3139a8-67e5-0310-9ffc-ced21a209358

* master:
  Change mean-dropout to mean-zeros
  Add verbose to scDDEstimate

From: Luke Zappia <lazappi@users.noreply.github.com>

git-svn-id: file:///home/git/hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/splatter@131415 bc3139a8-67e5-0310-9ffc-ced21a209358