Refs #30; Fixed label-less layers for basic line plot.
Refs #33; Fixes label-less layers for the basic area plot.
Refs #30; Fixed label-less layers for the basic bar plot.
Refs #30; Fixes label-less layers for the basic scatter plot.
Refs #30; Opted to always just use the category index when grouping data points in multi-series plots.
Refs #30; Fixed label-less layers for basic pie charts.
Fixed merge conflicts for the pie chart.
Merge pull request #39 from fastly/rsandor/fix-labeless-layers

Fixes #30 - Basic Plot "Label-less" Layers