Shedna/enable third party auth on studio

@talbs can you check for the buttons' style ?
@johncox-google if you wanna take an eye on this ?
cc @nedbat
Ok I understand what you mean, indeed there are no specific UX in CMS to manage third party auth grants. But since LMS and CMS accounts are link, at the moment it's possible for the user to revoke access from the LMS dashboard.