Support for WordPress 5.0 and the new block editor

[bobbingwide]

To support use of the new block editor we need to change the registration of the oik_testimonials CPT.
Add

$post_type_args['show_in_rest'] = true;

The testimonial_type custom category also needs to be show_in_rest. oik-testimonials will need to be dependent upon oik v3.2.4 or higher.

[bobbingwide]

When I enabled the oik-testimonials CPT for the block editor, with Gutenberg 6.1 I got a white screen of death.

index.js?ver=1562837440:1 Uncaught TypeError: Cannot read property 'displayName' of undefined
    at index.js?ver=1562837440:1
    at editor.js?ver=7.5.2:24
    at index.js?ver=1562837440:1
    at index.js?ver=1562837440:2
    at Array.map (<anonymous>)
    at ne (index.js?ver=1562837440:2)
    at index.js?ver=1562837440:14
    at Array.forEach (<anonymous>)
    at Sc (index.js?ver=1562837440:14)
    at Object.so (index.js?ver=1562837440:12)
(anonymous) @ index.js?ver=1562837440:1
(anonymous) @ editor.js?ver=7.5.2:24
(anonymous) @ index.js?ver=1562837440:1
(anonymous) @ index.js?ver=1562837440:2
ne @ index.js?ver=1562837440:2
(anonymous) @ index.js?ver=1562837440:14
Sc @ index.js?ver=1562837440:14
so @ index.js?ver=1562837440:12
(anonymous) @ post.php?post=814&action=edit:582

This is resolved by updating to Gutenberg 6.1.1 which has the following fix.
WordPress/gutenberg#16518