Add option to close Collapse when clicking outside of it

[LeBenLeBen]

The Toggle component would benefit from a new prop to enable auto-closing when the user clicks outside of the ToggleContent. This would be especially useful when used for flyover elements such as dropdowns.

[LeBenLeBen]

Since dropdowns will get a dedicated component (see #58) and this can already be done with the clickOutside directive, let’s drop this idea.