Add API to query the API call limit.

Add basic support to get the API limit as explained in issue #35. 

Summarized design:

1. Create abstract class `InstagramObject` which has methods to set `Response` and get the remaining limit and available limit.
2. All entities class that are created using `Instagram.CreateInstagramObject` extend from the new abstract class `InstagramObject` so that we can set the `Response` inside `InstagramObject`.
3. Client can query the limit after it creates the entities by calling `getRemainingLimitStatus` method.