LightPipeline annotate method returns unusable object

[dkincaid]

LightPipeline annotate method is currently returning an R list of spark_jobj objects. Somehow we should be able to convert these into lists themselves.

This is holding up completion of the ner_dl.Rmd example.

[dkincaid]

Feedback from Kevin:

A couple ways I can think of are 1) call mkString() with a separator and reconstruct a vector from it and 2) call .toArray in compiled code. The "better" way is probably adding the appropriate serde in the invoke() mechanism, and we can spend some time thinking about how that would work. In the mean time though I think you can pick one of the hacks and we can always refactor later.