Use field_extra_fields to be able to position the "Rich text editor settings" fieldset

Currently ckeditor just adds the "Rich text editor settings" fieldset to the user form with weight = 10. If the module would implement hook_field_extra_fields() to define the fieldset, we could position the fieldset within the form. Maybe always at the bottom. Maybe together with the Timezone settings in another fieldset. Etc.

This is how entity forms should be extended. And it's ridiculously simple. Just implement hook_field_extra_fields() and define a 'ckeditor' element. No change in the existing form alter. I'll create a patch later.