Rename module "about" to "info"

The latter is more representative of what is returned by this endpoint.
Separated "base" modules for webapp2 extensions

Moves the existing ApiResponse and ApiWSGIApplication classes out of the
root init module into a new "base" module, cleaning up the init module
considerably.
Common ApiRequestHandler base class

Introduces a new abstract base class that all request handlers will
extend from to automate some new functionality.