Minor source formatting.
Added a guard against a `NullPointerException` in `getPageText`.
Renamed `SubmitNewPageController` to `SubmitWriteController`.
Renamed `EditPageServlet` to `SubmitEditServlet`.
Renamed `EditPageController` to `SubmitEditController`.
Abstracted common servlet methods into a `SubmitServlet` superclass.
Added a default author name of "???" for logged out users.
Add a link to the first page in the story.

There are two bugs:

1. There should be no link to the first page if the page being viewed
already is the first page. (No need to link to the current page.)
2. Alternative versions all are currently linking to version ‘a’,
because the first page ID is not being saved correctly when the
alternative version is created.
Fixed a bug where the link to the first page pointed incorrectly to version 'a'.
Refactoring: pulled up many common submit controller methods.
The first page in a story now does not have a "return to beginning" link.
Refactor: Fixed magic number for maximum title length.
Refactor: `isContentValid` has been clarified to `isContentBlank`.

The return value is inverted because blank content is invalid content.