Ability to collapse namespaces in outline ▶

[juniorxsound]

Context

Right now there's a small triangle next to the namespaces (and other objects too) in the outline view that hints that by clicking it you can collapse it, however it doesn't collapse when clicked. It'd be really helpful to add the ability to collapse namespaces in the outline.

[clementroche]

Seems related to #255

[clementroche]

fixed by #367