jottacloud: support whitelabel service Phonero Sky

Phonero is a Norwegian mobile provider focusing on the enterprise
market. They provide rebranded Jottacloud service through their «Phonero
Sky» (Norwegian for «Phonero Cloud»).

The Client ID `desktop` used by most of the other whitelabel services
does not work for Phonero Sky. Both `desktop-win` and `desktop-mac`
work, though. Authentication does not work when the `jotta-default`
scope is present, so drop it. This results in a Client ID and scope
setup that is identical with that of Let's Go Cloud (Germany).
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