Bugfix - correct 'plotly-related' yPlot() jitter issue

[dtm2451]

Re-make of #9 since I built my own fix before seeing that version.

Per investigation by @j-andrews7, discovering the root cause of this long-standing dittoSeq-issue, adds a column to the data_frame when needed (group.by and color.by not the same) and uses that column or group.by for explicitly setting the group aesthetic for the jitter geom.

This PR also turns showing hover.data back on for yPlot

I had commented the code for utilizing this data out because of the bug addressed here!

ToDo

• add tests (and check again for other breakages)
• assess other do.hover behaviors to get that all more ironed out here
  • add hover.round.digits to control length of numeric values displayed
  • add group.by/sample.by/color.by to the data shown for barPlot() and freqPlot()
  • add presumptive default for scatterPlot() hover.data
  • document