improve error dialog if could not find helper running

many users are complaining about AV solutions blocking the helper (even though it supposedly comes clean on latest scans). I suspect outdated definitions, but that's another issue. About UX, right now the windows client only says "checking status" as feedback.

besides obviously avoiding the false positive (online installer superseding nsis installer), and better release management (avoid to drop unsigned installers in systems that have automatic sample submission enabled on their AV), I think we could try to diagnose the problem more accurately (ie, is the helper running? is it running an old version?) and give a more consistent message to the user (probably linking to an issue or suggesting some action, like reinstalling or reporting AV version and malware classification for dispute etc)