add label and size to scatter3

[felixcheung]

Minor update to scatter3 chart support in lightning-scala:

• add label array in API with default value
• add size array in API with default value
• convert both into lists and add to data map being passed to internal plot call

[freeman-lab]

Thanks @felixcheung ! Mind adding a description, just so others know what this is? I'll take a look and give feedback soon.

[felixcheung]

@freeman-lab just did. thanks.

[freeman-lab]

@felixcheung this looks great! Could merge as is, but would you like to quickly add alpha and color to the PR so we can get all options in at once? Alpha can be an Array[Float], and color should probably be Array[Array[Int]] or Array[Tuple3], whichever you think is better.