"Cannot read property 'icons' of null"
@Kevin are you sure the fix was due to CKEditor being upgraded in that Drupal version? I'm getting the same kind of issue trying to add the Link plugin, on Drupal 8.1.1, which is using CKEditor version 4.5.8.
Trying to find more insight on this issue.
edit: upon manually upgrading CKEditor to version 4.5.9 I'm getting much more illuminating error messages:

Uncaught Error: [CKEDITOR.resourceManager.add] The resource name &quot;link&quot; is
already registered.
Uncaught TypeError: Cannot set property 'getLinkAttributesParser' of undefined
Uncaught TypeError: Cannot read property 'icons' of null

So looks like this is colliding with the Link plugin that comes with Drupal (which is lacking some features). So I'll find a way to sidestep this name space collision and will update here.
edit: renaming the plugin proved unfruitful. Still getting:

Uncaught TypeError: Cannot read property 'icons' of null