Minor add adapter interface spec

The shared specs for the 'adapter' interface provide a better
help if they spot the methods which miss an override.

Adding this spec makes the shared specs no longer usable with
the `Adapter` module itself. Some more caution will be needed
to ensure both the module and the shared specs stay in sync, but
the module should change less often than new adapters will be added.
Minor refactor tidy up TokenAuthenticationHandler

Fix circular dependency (!)
Minor fix harmless variables shadowing in dynamically defined methods

Remove forgotten hack related to the deprecated Cucumber scenarios
Require ActiveRecord as development dependency

Fix Travis CI build, force `--no-deployment` installation

As long as an ORM/ODM/OxM is available, there should be
no obligation to install ActiveRecord.

About the Travis issue, see:
https://github.com/gonzalo-bulnes/simple_token_authentication/ \
commit/5c04e13c44379d95b95c1affcdb85177cf6188e3 and
https://stackoverflow.com/q/26221540/3767264