BUGFIX: removing reliance on Parent::getCMSFields

Removing reliance on the parent::getCMSFields within the getCMSFields method for the following reason:

- in line with the way CMS Fields are added by Folder, File, Group, SiteTree and other core classes

- faster (no need to add a whole bunch of fields and then remove them again)

- updateCMSFields only called once

- better organisation of fields with less relevant fields out of the way in separate tabs (locale settings), making the member CMS fields less intimidating and messy.