1161 bug new api duplicate links object in get one api responses

[osaerdna]

• Moved the data self reference from AbstractBaseAPI::obj2Resource to AbstractModelAPI::getManyResources
• Added tests for getOne, getMany and POST requests in test_http_methods.py

I have made some manual testing in the web-ui and cant see that anything breaks with the change.

@jessevz, please add other reviewer as you see fit.

[osaerdna]

The change in the api (no self reference inside the data entity) break the implementation of python-hashtopolis that relies on that one when creating objects. I will check if there is a way to implement a backward compatible fix, otherwise I would appreciate some guidance on how to move forward with this one.

[jessevz]

I have looked at the code and I think it might be better after all to keep the duplicate uri. it is only for getOne requests and by keeping it it is easier for clients to use the api and not have to switch between to many to one cases. Just like we see now in the hashtopolis.py case