RFC: Only place one "add tab" item in the Context View toolbar

[Nikolaj Hald Nielsen]

> When I enter the "config" mode of the Context View, I've noticed that
> I tend to forget to leave it again. Leaving it currently requires
> clicking the "Configure" icon explicitly.
>
> To fix this, we could make it close automatically as soon as you click
> any other part of the application. Say, when you click something in
> the playlist, the Context View configuration mode would be disabled
> automatically. I think that's the behavior that you would tend to
> expect. Staying in configuration mode then doesn't really help with
> anything, it's just confusing.

This makes a lot of sense as that is also how "normal" popup menus work.

- Nikolaj