Do not manage CPTs set to private

[jeherve]

When registering a CPT, WordPress allows you to define "private" CPT thanks to the public parameter:
https://codex.wordpress.org/Function_Reference/register_post_type#Parameters

When a CPT is set to private, its UI is not shown on the site's frontend. I would consequently not expect that CPT to appear in the Custom Post Type Permalinks plugin interface.

Would it be possible to exclude such CPTs from the plugin in the future?

Thanks!

Reported here:
https://wordpress.org/support/topic/jetpack-plugin-adds-sidebars_widgets-and-widget_image-links/

Related: #76

[torounit]

@jeherve Thanks Feedback. I want to fix next version.