Add granular permissions for navigation/menu bar

[tom0010]

Plugin Version

0.5.1

Proposed functionality

When adding permissions for a user to not allow branching capability, the app/plugin still shows on the navigation bar. If you click "Branches" or "Change Diffs" you get a friendly error page saying: "You do not have permission to access this page."

I am proposing to add extra permissions to navigation.py so when a user does not have permission to see the branching plugin, it will be hidden.

If accepted, I am happy to write a PR for this.

Use case

This offers better UX, users will not see the plugin, and it will look a lot cleaner overall.
There is no point in showing entries in the navigation bar when they cannot be accessed.

External dependencies

No response