[DMN Designer] Prohibit parallel item definition edition

We should prohibit parallel edit operation of item definitions in managa custom data type dialog. It brings troubles in different scenarios:

Save parent item

1. Open attached dmn model
2. Invoke manage custom data type dialog
3. Expand tProfile item
4. Click on edit next to tProfile (Structure)
5. Click on edit next to Name (string)
6. Change Name to Name_updated
7. Change tProfile to tProfile_updated
8. Click Save next tProfile_updated
9. Save button for Name_updated will disappear
10. Changes saved just for parent item tProfile_updated

Save referred items

1. Open attached dmn model
2. Invoke manage custom data type dialog
3. Click on edit next to tGender (string)
4. Click on edit next to tGenders (tGender)
5. Rename tGender to tGender_updated
6. Click Save next tGender_updated
7. The data type select box for tGenders will disappear, see
   1.