Show all top level custom Data Types in the dialog, instead of only the selected one

Show all top level custom Data Types in the dialog, instead of only the selected one. Even when the user does not have any ItemDefinition, the dialog must lunch.

Acceptance test

• No definitions present
• Invalid definition present
  • defined item definition for non existing feel data type: feel:ssstring
  • when editing no error shown
  • Nothing selected swhon
  • probably ok
• More than 20 definitions present
  • Able to scroll
  •