[DMN Designer] Differentiate zero and non zero custom data types

There is no visual information if no custom data type is defined. In the attached dialog we should differentiate between states when no custom da taype is declared and when some custom data types are declared. The same way we do it in list of spaces and list of projects.

Manual acceptance test

• Create new model, empty state indicated, save and reopen
• Create some data type, not empty state indicated, save and reopen
• Remove the data type, empty state indicated, save and reopen
• Firefox, Edge, Chrome