Option to run in background notification instead of foreground spinner

[snarfed]

Right now, in many situations HTTP Shortcuts uses a foreground spinner to send the network request. Totally understandable, but it blocks other user interaction with the phone until it's done. I'd love the option to use a background notification instead!

More background in #228. @Waboodoo says this or something like it is planned eventually, so I'm just filing this to track that. Hope you don't mind. Thank you again for HTTP Shortcuts, it's great!

[Waboodoo]

As of version 3.11.0, there is no an experimental option which allows running all shortcuts in the background instead of the foreground. It might solve this issue. I'm hoping to further improve this and make it a proper feature with more options eventually.