htmltools integration

[cpsievert]

Left TODO:

• Register any attached html dependencies
• Translate htmltools::HTML() to https://github.com/plotly/dash-dangerously-set-inner-html
• Compelling examples that translate shiny ui to dash layout
• Tests

[chriddyp]

Translate htmltools::HTML() to https://github.com/plotly/dash-dangerously-set-inner-html

Is there a way to use the dash-html-component library instead? we should really avoid using dash-dangerously-set-inner-html since it's really easy to shoot yourself in the foot with XSS.

[cpsievert]

Might be, but it wouldn't be straightforward -- I'll think about it more when I come back to this (probably in a month or so)