This updates WebAPIResource to add typing and documentation for the

attributes intended to be filled in when subclassing. This can help with

ensuring that subclasses properly configure new API resources.
There is the usual issue where some attributes (name, name_plural,

and some others) are defined as properties by default, and overriding

them causes issues with the type checker. This is a wider problem in how

we manage configuring subclasses, and won't be addressed as part of this

work.

Unit tests pass.