Run user defined command when clicking on plasmiod

```
It would be helpful if a user defined command could be set to run upon
clicking the plasmoid. For example, when the plasmoid is docked in a panel,
clicking it could load Gmail in Firefox or Konqueror.

```

Original issue reported on code.google.com by `mjmcc...@gmail.com` on 29 Jan 2009 at 11:20
