* standardise plot data output
* add data required for new anchors to renderer properties
* feed dvc-render updates into API output
* update --json --split api with new data types (send split anchor definitions as strings)
* accomodate zoom and pan anchor
* switch anchor_revs to revs_with_datapoints
* accomodate height and width anchors
* drop terrible idea of holding all data as strings
* fix plot having multiple x fields
* move inferred properties off vega converter class
Matt Seddon