Collection of UI bugs

[lsd-cat]

Here is a collection of tests to run and known bugs of the UI, which logic will probably have to be changed:

• main_frames can be reloaded by a worker, and thus a tab can be reloaded, but the tabId will be -1, leaving us unable to determine which tab to update (it's the case when joining a Jitsi room).
• not in all error cases the user is properly redirected to the blocking page
• we need to determine how to display the presence of (verified) external sources or iframes

[lsd-cat]

How to display resources loaded by iframes and serviceworkers is also a topic.

[lsd-cat]

Show external sources in popup: 90aba54

[lsd-cat]

• not in all error cases the user is properly redirected to the blocking page

Also fixed during one of the recent refactoring afaik.