Added extension/theme Campaignify.
First init post types, higher priority (from 20 to 0).

Priotiry of the initial post types function should be set to < 10

@see https://core.trac.wordpress.org/ticket/28488
@see https://core.trac.wordpress.org/changeset/29318

@see https://github.com/WordPress/WordPress/blob/4.0/wp-includes/post.php#L167
Adjusted tested up to Easy Digital Downloads version.
Set errors if an error occurs.
Use the new Easy Digital Downloads library from the wp-pay-extensions/easy-digital-downloads library.
Added an new iDEAL icon for Easy Digital Downloads.
Getting ready for version 2.9.0.
Improved the installation description, we now also mention the requirement of an e-commerce or forms plugins.
Moved meta box files to the admin folder.
Let users specify the transition reference template.
Removed transaction reference options.
Tweak - Gravity Forms AWeber Add-On - Improved support for delayed subscriptions.
Updated Composer lock file.
Updated change log.
Merge branch 'release/2.9.0'