Refactor all functions in app to use BaseHandler methods

* Make all function in the `main.py` file use the `query` and `sort_results` methods of the `BaseHandler` class
* Reorder the parameters of the `query` method so that `payload` is optional
* Make all functions run out of the `main.py` file, thus making `ghrequests.py` redundant
* `ghrequests.py` has not been deleted as of yet, since it may be useful for future reference