Code improvements BAConnector.

In general I have only cleaned up code in the __BAConnector__ without adding new features or fancy stuff. 

I have introduced a service for creating GET and POST requests, since I didn't like the code repetition in __BAConnector__ (There is still too much, I think). 

I have also changed the way the JSON arrays are put together from NSArray content. The boolean _first_ is unnecessary from my point of view and I hope the way it is written now readability has improved. 

If you have any remarks, let me know.