Replace Vidalia's green onion feature

Vidalia’s green onion is buggy in various ways such as:

• It turns green a while after Tor is usable;
• Users (and even Tails developers) mistakenly believe that yellow means “bootstrapping Tor”, and even our doc is wrong about it;
• If Tor gets offline for some reason (e.g. bridge is down), then the green onion stays.

However, once we get rid of Vidalia (#6841 (closed)) we still want to keep such a permanent “Tor status” indicator on the desktop.

On the long term, we have ideas to make the green onion better, but that’s not blocking #6841 (closed): simply replacing what Vidalia gives us, with minimal efforts, and possibly with the same bugs, will be enough.

The design we’ve come up with is a minimalistic GNOME Shell extension that learns about Tor’s on/off state by monitoring whether a given file exists. The very same mechanism that currently displays the “Tor is ready” notification in Tails would create that file, that would update this onion.

Note that this green onion should not have an ugly white bar as some people see in Windows Camouflage mode (#7400 (closed)). Ideally, it would also use some less conspicuous stock Windows systray icon.

Feature Branch: feature/6841-replace-vidalia

Parent Task: #6841 (closed)

Related issues

• Related to #7437 (closed)

Original created by @intrigeri on 9002 (Redmine)