The StoryPage can now be read from the datastore.

* Added a `read` function, which retrieves the `StoryPage` properties
from the datastore and adds them to the `StoryPage` object.
* Added a `text` member field to the `StoryPage` which represents the
body text of the story page.
* Added a unit test to confirm that the story page is created in the
datastore and then read correctly.
* Minor editing of comments.