Workflows holdingpen changes

Hello:

Here are the latest changes to the Holding Pen that @dinossimpson have been working on. I merged it with the new structure and I hope it works (no way of testing the UI due to my current problems, see #49).

I discovered that in these changes we do need autodiscovery of widgets in the holding pen. So for now I kinda reverted to the old method as I am not sure which method is going to be the preferred way in next.

Cheers,
Jan