Make progress of async command visible

[manuel-mauky]

At the moment the commands have a runningProperty. When using Async commands we can use this to show a loading indicator.
But in some use cases I would like to show the progress of the command with a progress bar. In this case a boolean isn't sufficient. Instead I need a percentage value (double).

[sialcasa]

• first thought: sounds like the Task interface with executable extension ^^
• second thought: its not like the Task interface, because the valueProperty is not MVVM conform (Value list is in the ViewModel and should not be in the Task)

[manuel-mauky]

This will be possible with feature #225.
Therefore I'm closing this issue now.