Provide visual indication that watchbind is currently blocking

[fritzrehde]

For blocking subcommands that execute for a very long time, it is often unclear whether the subcommand is actually still executing, or whether it has completed. Therefore, it would be useful to have an optional UI indication that watchbind is currently blocking. The reason I would like to make this optional (ideally, this would be an option set directly in the keybinding, so next to the operations that would execute for so long) is because most blocking subcommands are probably executed very fast, which would cause the UI indication to appear and disappear very quickly, which would be observed as a flicker. Therefore, the user should decide themselves for every operation it the UI indication should be shown. An alternative would be to only show a UI indication that watchbind is currently blocking if the command has executed for more than a certain customizable time. However, I am worried that this is not a very deterministic solution, since commands run at different speeds on different computers.