SplitScreen with nav_bar and tab_bar

Here are a patch how I can use nag_bar and tab_bar with SplitScreen.
Opening new DetailScreen with a normal open.
Possibly I have overlooked this functionality in 0.6.

Example:
```ruby
open_tab_bar(
  create_split_screen(
    ListScreen.new(nav_bar: true, title: "List"),
    DetailScreen.new(nav_bar: true, title: "Details")
   ),
  OptionsScreen.new(nav_bar: true)
)
```