Do not allow installing GitHub applications

[bjohansebas]

Well, I've seen that some organizations block the installation of GitHub apps, and only an admin or owner can install them.

It would be good to prevent just anyone from installing GitHub apps, since not all of them are safe — some can have access to important parts of a repo or other sensitive things.

We should check if GitHub provides an API to verify this behavior and think about a good implementation for VisionBoard

[UlisesGascon]

I like the idea! 👍