Further improve netkan relationship error message

[HebaruSan]

Motivation

#4020 replaced the very unclear "Specified cast is not valid" message with a proper schema validation error. On further consideration, the schema error still isn't clear enough, because it doesn't explain why the array item is not valid.

1717 [1] FATAL CKAN.NetKAN.Program (null) - Schema validation failed: #/depends[0]: ArrayItemNotValid, #/depends[1]: ArrayItemNotValid, #/depends[2]: ArrayItemNotValid, #/supports[0]: ArrayItemNotValid, #/supports[1]: ArrayItemNotValid

Changes

Now the RelationshipsValidator explicitly checks the type of the elements of relationships arrays and prints a message that hopefully will be clearer:

$ netkan.exe NetKAN/kOS-KerbalEngineer.netkan
507 [1] FATAL CKAN.NetKAN.Program (null) - depends elements should be Object, found String: "KerbalEngineerRedux"