Support nested points in views

[bkutil]

These views should be able to handle points whose values are objects/arrays, or report an error about being unable to display them (list was taken from the online docs, please update if something is missing):

• [ ] barchart
• [ ] events
• [ ] less
• [ ] file
• [ ] piechart
• [ ] scatterchart
• [ ] table
• [ ] tile
• [ ] timechart

refs: https://github.com/juttle/juttle/issues/55