Dataflow-specific builtin cell

[asg017]

A builtin cell named dataflow that have some Dataflow-specific utility functions and constants.

dataflow.theme

A string that updates whenever a user updates the "theme" of a notebook, ex dark -> light or light -> custom theme. #9

dataflow.grid

Object with utilities for the dataflow grid system, #22 .

dataflow.grid.get("myGrid").observeWidth("sidebar");
dataflow.grid.observeWidth("myGrid", "sidebar");

^^ how will this work for compiled notebooks?