Description of problem:
There is a document about how to define "Work item definition" on business-central, but not for JBDS process designer.
https://access.redhat.com/documentation/en-US/Red_Hat_JBoss_BPM_Suite/6.0/html/User_Guide/sect-Domain-specific_Tasks.html#sect-Work_item_definition

Expected results:
This is the instruction for JBDS process designer:

• Create WID_NAME.wid file under $PROJECT_HOME/src/main/resources/META-INF
• Content of WID_NAME.wid is same with the one for business-central
• If icon's path is like "icon/notification.png", create icons directory under $PROJECT_HOME/src/main/resources/, and store image files in icon directory.
  Once you save the file, you can use your custom service task with JBDS process designer. You can find yours at "CustomTasks" category on a pallet.