Adding filter to $this->default_post_types

[ryanwelcher]

Adding a filter to allow other post types to be used

[mjangda]

Since the root issue is that the default_post_types property doesn't updated when additional post_types are added/removed from zoninator, we should fix that instead. Otherwise, we make adding post_type support even harder (you have to call add_post_type_support AND filter this AND ...).

[mjangda]

Admittedly, this filter makes it pretty easy to add post type support but goes against the typical WordPress-way of adding post_type support. I think I'll need to think on it or additional feedback/viewpoints :)

[bcampeau]

:+1: to @mjangda I agree on that

[ryanwelcher]

Thanks for your feedback! I have taken a different approach based on your comments and issued a new pull request on a different branch - #34