Massive changes abound to support 10.1+

- Changed get_all in each class to @classmethod instead of
@staticmethod, to allow the passing in of resourcetype for use in the
Content-type construction

- Updated tests.py slightly to include a logout

- Converted all HTTP verb functions in nsnitro.py to also accept the
passing in of a resourcetype, to allow for the construction of the
Content-type header on a per-request basis without having to
deconstruct the URL that gets passed in.

- Working on less reliance on the NSNitroResponse library, and instead
on using the Requests library to provide JSON parsing functionality
in-function.

There’s probably many better ways to do a lot of this; suggestions
welcome.