I will

I forgot to say:
I think most of the GUI is self-explanatory. There's only one point:
When you add a field of type combobox to the defaults or to an item you have to insert a comma separated list of possible values you want to select from. The first one will be the default value.
Shame on me, but you have to insert a space after each comma. I'll fix it soon.

Please, try my app and post you comments!