DetectCustomPostTypeURLs returns URLs for almost all post types

[Flynsarmy]

This is a problem because that includes built-in ones such as Post - making this detector return a potentially HUGE list of duplicate URLs to the DetectPostURLs detector.

There are a few things we could do here.

• Exclude all built-in post types OR
• Rename the class to DetectAllPostTypeURLs and just cover everything in this one class.

[leonstafford]

Exclude all built-in post types

Would be my preference, to keep more granular control and allow users/addons to toggle it with filters