Add support to consume input schema having propertyKey's cardinality as LIST

[leichuan]

According to users_guide.md, the cardinality of propertyKeys can be chosen from <SINGLE|LIST|SET>. However, the BatchImport can only support SINGLE, not LIST nor SET. For example, a user in the twitter example can have multiple addresses, phone numbers, etc.

[madhuvasu]

Hi, are there plans to support the above? Thanks.

[madhuvasu]

@yhwang Any plans on supporting this feature..? This would be quite useful. Thanks.

[tedhtchang]

@madhuvasu This is a good feature and actually want to make our csv generator to support this feature as well. We need to study how csv file support list/set and check if our importer can support it. Have you done this before?

[yhwang]

not sure if common-csv support format like this:

valueA, valueB, [ listvalue1, listvalue2 ], valueC, valueD