Add assign dropdown id and change default to $group_$name.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Add assign id description to readme.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Add assign id to example.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Change data seed key to represent object rather than level.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Add assign predefined value for dropdown.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Add assign predefined value example.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>
Add assign predefined value documentation to example and readme.

Signed-off-by: Hendra Uzia <hendra.uzia@yahoo.co.id>