Display a warning notification if the new identity feature is used

If it is possible to detect that the new identity feature has been used (either the one from the browser or from Vidalia) then we could display a notification pointing to our warning about identities.

First we should quickly investigate how feasible this is…

Related issues

Related to #5716 (closed)
Related to #7226 (closed)

Original created by @sajolida on 7471 (Redmine)

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