Default show_in_nav_menus to false if not set

[bobbingwide]

When registering CPT's and custom taxonomies using oik APIs it makes sense to set show_in_nav_menus to false if the value if not defined by the caller. This will reduce the number of custom variations for the core/navigation block.

See bobbingwide/oik-types#23 and bobbingwide/oik-blocks#49

Proposed solution

• Change bw_register_post_type(), bw_register_custom_tags() and bw_register_custom_category()

[bobbingwide]

Developed in oik v4.6.0, released in oik v4.7.1.