Add visual tests for all libraries

[ramnathv]

Right now I have examples.R which tests different type of charts. However, I need to do this more systematically with a test suite that tests different aspects. Here is an example for MorrisJS

dat = subset(haireye, Sex == "Female")

## test that labels default to group names when not provided
p2 <- mPlot(Freq ~ Eye, group = "Hair", data = dat, type = "Bar")
p2$show(T)

## test that label argument is respected when explicitly provided
p3 <- mPlot(Freq ~ Eye, group = "Hair", data = dat, type = "Bar", 
  labels = letters[1:4])
p3$show(T)