Support setting layout of charts

[mightyguava]

There doesn't seem to be any way to define layout for charts, e.g. width, height, which row has which chart. Did I miss it? Or is it missing?

[greatestusername]

This is not possible with the "simple" endpoint that we currently use.

Docs available here: https://developers.signalfx.com/dashboards_reference.html#tag/Create-Simple-Dashboard