Missing event when colorbutton plugin is activated

[Axel Nerlich]

We need an event that is always fired before a plugin is activated (in other words a toolbar button is clicked). Most plugins are implemented as commands. For those cases the beforeExecCommand is a viable option. The colorbutton plugin is not implemented as command. It should either be implemented as command or fire a specific event in its onOpen event handler.

[Jakub Ś]

Event fired in onOpen method sounds like a good idea to me.