Clean up various bikeshed issues, remove a lingering id reference, and update permissions integration

[inexorabletash]

• The definition of screen id was still present, but unreferenced. Remove it until we need it.
• Simplify how permission is queried, using recently updated specs as a model.
• Use the enum entry for "denied" string
• Fix linking to Window's open()
• Drop reference to resolved issue #54
• Update "powerful feature"+"boolean feature" to "default powerful feature"
• Add (commented out) sketch of Permission Policy integration
• Remove blank lines around list of contributors (in rendered output)
• Credit @quisquous !

@quisquous - can you take a look?

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