Multi screen playlist
The multi screen playlist is a special playlist that can display two different slides on two screen at once
with a single click.
Each row represents what will be played to each screen.
By clicking on a slide it will be shown on its screen
By clicking on a the column header both slides to both screen will be played concurrently.
If the second row is not filled the slide in the first row will be shown on the second screen
The concept is that the first row is primary, and needs to be defined. The
second row is optional for when a different slide is required to screen 2
The left and right arrow keys navigate through the playlist. Clik on the playlist so this
has the keyboard focus

Note
This does not currently support adding notes to slides