New classes for the Portfolio Board endpoints

Adding Classes for the Portfolio Board endpoints (#45)

* Add Portfolio Board Model

Add the Model for the /portfolio/boards endpoints for the Teamwork API
https://developer.teamwork.com/projects/portfolio-boards/boards-in-portfolio-view

* Add Portfolio Column Model

Add the Model for the /portfolio/columns endpoints for the Teamwork API
https://developer.teamwork.com/projects/portfolio-boards/columns-inside-a-portfolio-board

gatAll / insert use this end point: /portfolio/boards/{boardId}/columns

* Change getAll to getAllForBoard in Column

The getAll method wasn't really correct, as there isn't a get all method.

You can only get all columns for a given board (the ID of which was
already being passed in), so added ForBoard to the function name

* Add Portfolio Card Model

Add the Model for the /portfolio/cards endpoints for the Teamwork API

Some use special endpoints:
- getAllForColumn: portfolio/columns/{columnId}/cards
- insert: portfolio/columns/{columnId}/cards (this adds a project as a card on the given column)
- update - portfolio/cards/{cardId}/move (this moves the card from one column to another)

v1.2.0: Changes to the notebook call (#39)

* Changes to the notebook call

Added ability to update an existing notebook and updated api fields