Add a separate function for sidebar navs

Right now, you can place tabs on the side of a dashboard layout by specifying `tabsOnSide=true`. The problem is this argument is leaky as it then changes the behavior of where things are placed with the `after_navigation` slot/argument. It also is a worse fit for additional sidebars etc. 

For simplicity's sake, there should probably be a `_vertical_nav` variant for all the tab-aware containers. 