BS4 Alpha 5 Omissions

Created by: srvance

I'm in the process of porting ember-bootstrap to be BS4-friendly. We would like to have it mutually compatible so we don't force everyone to move. In most cases, we've been able to successfully do that. There are two omissions that we would like to have filled in or documented in the migration doc.

The icon-bar style has been removed. It's easy to re-create, but I'm sure lots of people have used it.
Tabs have been removed. Comments in other issues seem to indicate that Navs with tab style should be used, which is a useful building block but doesn't address the pane switching. The migration guide refers to panels, but that's not what the tab panes are called, so I don't know if this is related or not.