CiviCRM-WordPress - Gutrenberg Compatibility: Do not parse shortcodes in REST context

WordPress 5.0 will introduce a new default editing experience. The code name is 'Gutenberg' . Gutenberg is built on blocks and the method of handling modals in the editing experience is changing.

The existing modal for inserting shortcodes will not work with Gutenberg. We will need to rework inserting the shortcode to a new block for the new release. Expected Merge Request for Gutenberg will be April 2018 and the release will be sometime thereafter.

However, this week WP 4.9.5 will ship and in this release will be a call to action to all users to install the Gutenberg plugin to test.

Currently if a CiviCRM shortcode is put into the 'Shortcode Block' there will be an error and the post will not save properly. As bastienho points out in PR 126 the following error is thrown: Notice: Trying to get property of non-object in civicrm/civicrm/CRM/Utils/System/WordPress.php on line 221

For now we should fix this error and then work on full Gutenberg Compatibility once the official merge request is approved to WP.