Feature request: Configure expand/collapse state for navItems of c-sidebar-nav

[bernik1980]

If you specify children for an INavData item, a expanded dropdown will be displayed in the navigation.

Currently, these dropdowns will always be expanded.

It would be really cool, if ...:

1. ... there would be a property to specify the intial state
2. ... there would be a callback if a state did change, so can save this state for the next load

[bernik1980]

And as a side note for this matter: Switching "dropdownMode" values does not have an impact on the functionality, it always behaves the same