confgen: populate the field with the key's first row by default on aggregation

[wenchy]

Aggregation Problem

• scalar field Name, last overwrite wins, so the final value is "chapter11".
• list field Group, by default, will aggregate multiple rows, so the final value is [1,2,3,1,2,3,1,2,3]

ChapterID	Name	Group	SectionID	SectionName
map<uint32, Chapter>	string	[]int32	map<uint32, Section>	string
Chapter's ID	Chapter's name	Group IDs	Section's ID	Section's name
1	Chapter1	1,2,3	1	Section1
1	Chapter1	1,2,3	2	Section2
1	Chapter11	1,2,3	3	Section3
2	Chapter12	5,6	1	Section1

Solution

Populate the field with the key's first row by default on aggregation, and report errors if corresponding cell data in the following rows is not same as the first row.

• scalar field Name, report an error due to the last name Chapter11 is not equal to Chapter1 at the first row, and if fixed, the final value is "chapter1".
• list field Group, the final value is [1,2,3]