Display arbitrary wallpaper

[jagmit]

Context

In our Gurdwara Granthis, Kathavaachaks etc. often request a certain wallpaper to be displayed during their stagetime. Usually it's a historic painting which depicts a Guru, Bhagat or ithiaasic event which the Kirtan, Katha etc. will be about.
For the old PowerPoint based sttm our workflow used to be to set the wallpaper as the desktop background. This way it would be displayed in between shabads. For the newer sttm this workflow is a bit tricky because the presentation window stays open eagerly even "in between" shabads and it is not designed to be dismissable.
Setting up the wallpaper as a custom theme background is not an option because the wallpapers usually make up for a bad backdrop for text because of high contrast etc.

Suggestions

• The new "HIDE SCREEN" button could cause the presentation window to become translucent instead of turning black so that the desktop wallpaper from "underneath" could become visible.
• Another solution could be to add a custom image option to the "Insert" tab, where any arbitrary image could be selected from the local drive. One disadvantage is would be that sttm would need to re-implement all the displays options macOS and Windows provide to control the placement of an image:

Windows 10 UI

• Allowing to minimize the presentation window could also be an option.