Generate sql fixes
- Fix invalid sql produced for serialization of objects with belongs_to associations and includes set to true
- Fix DuplicateAlias error when table has more than reference to a second table
- Fix issue where relation.dup.arel_table.name can be empty string when app first starts
- If sideloaded table is empty should return [] instead of null (matches activemodel serialization behaviour which frameworks like ember expect)
- Use json_agg if available
- Change sql computed properties on serializers to be instance methods, means current_user alias can be used