Allow for removing the inset in 2htdp/universe

[a11ce]

Currently, 2htdp/universe adds a small inset to the drawn image. For example,

(require 2htdp/universe
         2htdp/image)

(big-bang (square 100 'solid 'purple)
  [on-draw values])

looks like this:

The inset is defined here and used here. I want to add the ability to turn off this inset (or to remove it as an option, but presumably whoever added it has a different aesthetic opinion).

Would it be best to add it as a big-bang clause? That doesn't seem ideal as it's not really a significant decision. Maybe a different display-mode option ('borderless)?

I'm happy to make the change but I know htdp has special design considerations so I'm asking how to proceed.

[mfelleisen]

If I recall correctly, I added the INSET in response to another user. I am not sure turning it off deservers a world clause because this is just not at the same conceptual level as existing clauses. (These clauses make up an ontology of specifying the world, not really its appearance.)

If this is for use in plain Racket, it might be best to export a parameter that allows disabling the INSET.

If this for use in *SLs, I'd be reluctant to change this.