Make the "x" argument of the plotly_sugar functions (such as as scatterPlot) optional

[AngelEzquerra]

Currently you must provide both the x and y arguments to most of the plotly sugar plotting functions. Sometimes you just want to plat a sequence, and you don't really care about the x-axis. It would be nice if the plot sugar functions such as scatterPlot*(x, y: untyped) could also be called with a single argument (y), which would just plot the values on an axis that started at 0, for example.