Better onboarding communication regarding optional permissions / access (file: URLs, private tabs, privileged pages).

[hackademix]

Follow up from #428

The fact full NoScript functionality require access to resources which are forbidden by default and require explicit consent from the user, such as file: URLs (Chromium only), private tabs and privileged pages may result in confusing experiences and breakages.

We should try to detect such situations and communicate them with as much clarity as possible.