Add labels to scatterplots

[cmeyer63]

If a data point includes a "label" field it will be rendered centered at that points (x,y) coordinates on top of the symbol. In the event the symbol's diameter is smaller than the rendered text, the text will be rendered below the point.

[palantirtech]

Thanks for your interest in palantir/plottable, @cmeyer63! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[themadcreator]