Support Private Repositories

[mfellner]

Allow users to add the repo scope in order to use Zappr with private repositories. This scope gives full access to private repositories thus we must not add it by default.

Dependencies

• Require less permissions for Zappr #90
• Delete GitHub data once we lose access #329

[prayerslayer]

For Enterprise installations it would be already sufficient to just drop/change the visibility parameter from here?

[j0k3r]

@prayerslayer it's all the case for non Entreprise install.

Switching the GITHUB_SCOPES isn't enough this line should also be switched to all instead of public.
Maybe this line can be switched to all for every one. Scope will limit private repo to show up.

[prayerslayer]

Yes, true, we also need to change the scopes. However in Enterprise installations you provide the configuration yourself anyways, including scopes to request. For Github.com we really need to do #90 first.

I'd expect all to work too.

[mfellner]

Closed with #406