Compare two charts about manipulatewidget HOT 2 CLOSED

Add a parameter .compare that accepts a named list with the values of parameter for each graph:

manipulateWidget(
  myPlotFun(commonPar, indPar1, indPar2),
  commonPar =mwSelect(...),
  indPar1 = mwSlider(...),
  indPar2 = mwText(...),
  .compare = list(indPar1 = c(1, 2), indPar2 = c("a", "b"))
)

from manipulatewidget.

• Add doc for new parameters
• Improve a bit visual aspects (add separations, improve alignement, etc.)
• Add examples in README and vignette
• Add a variable .id = 1 for first chart, 2 for second chart
• Manage the case where .compare is a list of length 0
• Change default viewer

from manipulatewidget.