Refactoring QueryCriteria unit tests to share a common abstract base class
#19 Correcting existing date-related tests to ensure UTC time zone is used - tests now  failing
#19 Adding (currently failing) unit test for addAttributeValue in AbstractDynamoDBQueryCriteria to ensure a single date criteria is serialized to UTC date format
#19 Adding fix as suggested by rshan2 to correct issue of date query criteria not being converted to UTC date format strings correctly
Adding (currently failing) test for addAttributeValue in AbstractDynamoDBQueryCriteria to cover scenario where attribute value is a list of dates
#20 Correcting typo in AbstractDynamoDBQueryCriteria.addAttributeValue method