feat(signage): add widget support

[stakach]

This way a display is drawn would be as follows:

• black background
• background_item (if defined)
• layouts in order, so full bottom bar, then side bar sitting on bottom etc
• remaining space is the signage player
• if the template is changed, don't restart the player, just reposition it on the new layout (would be cool to animate layout changes) as they can be scheduled