CKEditor shouldn't be manipulated in actionButton.js

As pointed by mflorea in https://github.com/xwiki/xwiki-platform/commit/6ccc4d5bda7edf551e0218578b48233a4f394d02#r33460339 actionButton.js shouldn't be aware of CKEditor.

Moreover, now that the conflict window does not just block the user from editing (starting with XWIKI-16346) it does not make sense anymore to set flags for the editor. So I propose to fix that by just disabling/enabling the action buttons themselves.