Allow user to edit properties of workflow inputs/outputs (at least domain properties)

[jeffbaumes]

It's a question whether the user should be allowed to also change the type/format, since that is bound to what it's connected to in the workflow. But the user should be able to change domain attributes like the referenced table for a column string property, or change a fixed list of options.

They should also certainly be allowed to edit the input/output names, which is also not currently available.

See #114 for more details.