Refactoring towards multiple engines

There are two concepts:

1) Multi Authentication
2) Orcid integration

The Orcid integration would become dependent on Multi Authentication.
Extracting Authentications controller

This will be part of Devise::MultiAuth
Extracting Authentication to Devise::MultiAuth
Preparing extraction of User methods
Removing dependency from User for Auth

Relying on Authentication.find_user_by… method
Removing User.authentications definition

I'm not wanting to pollute User with the other stuff.
Replacing Authentication constant with lookup
Extracting authentication towards configurability
Extracting specs for Devise::MultiAuth
Expanding tasks to run all contained specs
Updating devise-multi_auth.gemspec to be valid
Fully extracting Devise::MultiAuth engine
Removing spec:plugins from travis

This won't work
Removing spec tests for plugins
Tidying up object boundaries
Switching to public facing method

Instead of relying on a .call of a constant, expose a method.

Script
$ rails g devise:multi_auth:install
Cleaning up duplicate name
Tidying up default rake task
Adjusting migration table names
Moving devise-multi_auth