Revert "Revert "Added "lookup" and "new_item" to dynamodb2.table, which makes it more""

This reverts commit d4a2d7979752db79995530436813a5c9822802c4.
Switched to not specifically naming hash_key and range_key, which allows
for a more robust schema support in DynamoDB.
Added simple unit tests for the "lookup" function
Merge branch 'ddb2-port-lookup' into develop
Fixes #1780.