Minor refactor move spec helpers
Add TokenAuthenticationHandler public interface specs
Refactor extract TokenAuthenticationHandler

Refactor rename `define_acts_as_token_authentication_helpers_for`
to `define_token_authentication_helpers_for`

Refactor extract method `set_authentication_hooks`

The module specs are largely copied from the specs of
ActsAsTokenAuthenticationHandler. In order to keep the diffs
readable, I'll clean those in the next two commits.