Editorial: rewrite permissions section

[marcoscaceres]

The permission sections was confusing features and permissions.

APIs can be classified into powerful features, but only the permissions matter.

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[himorin]

needs to update hash at https://github.com/w3c/deviceorientation/blob/41a27ecb1e87637277098f6b948e37d3f7bcb39a/index.bs#L653 also

[marcoscaceres]

Rebased...