Unable to use `show_if` on imported settings

[hughsk]

The following code in settings:

- property: arc.palette
  show_if: arc.arc_palette_color
  import: "@flourish/custom-colors"

Leads to this error:

😱  Failed to reload template
😱  template.yml: Unexpected property 'show_if' in import

Unsure if I'm going to end up using it this way this time, but it might be useful in some cases?

[robinhouston]

Nice idea!