Cannot right-align NavBar items

[keeferrourke]

Looks like there is no way to add right aligned components in our NavBar, since we only use a single LEFT aligned NavbarGroup (ref).

We should keep the HomeLink in the left aligned group, and put children in another group where we can specify alignment.

TODO:

• Export a NavbarGroup component from @misk/core so that we can keep theming consistent
• Allow right aligned navbar_items in a second group