Persistence of enum choices in Commands

[stefanhahmann]

With 664b3ab and 61e98d7 it was made possible to use enums with custom labels in scijava commands

However, currently enums with custom labels are not persisted, i.e. if the user makes some settings using an enum with custom labels in a dialog, closes this dialog and comes back to this dialog, the selected value would fall back to the default parameter instead of the last selected parameter, which users may consider a bug, since this behavior would be different to other parameter types.