[BUG] Cross-reference to iSSEu issue 57

[kevinrue]

Cross-reference to iSEE/iSEEu#57

[kevinrue]

• Use this class to determine which dot plot creation utilities need to be added to iSEE. Obvious candidates are utilities to set font size or to add the coord_cartesian layer.
• .addFacets should probably operate more like .addMultiSelectionPlotCommands in terms of taking a commands= and slapping a + to the end to modify the ggplot construction.