Show notice about preferred support if `@supportURL` exists

* Use a "Well done" notice so we don't scare people off.
* Make this dismissable... some chatter on USO had ppl complaining about those not being dismissable

Applies to #239

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[![click to enlarge](http://www.picpaste.com/extpics/issue-239imp.png)](http://www.picpaste.com/issue-239imp.png)