[WIP] Composite auth adapter

[weierophinney]

As originally proposed in #65

This PR adds the possibility to use multiple authentication adapters under the same type.

It also introduces an AdapterAbstractFactory that allows to retrieve each adapter from the ServiceManager under the naming convention zf-mvc-auth-authentication-adapters-{type}.
This enables a new method to register custom adapters: using a service name the adapter key of a named adapter configuration.

TO-DO:

• Provide a way to use the composite adapter as a default one for all APIs
• Integration Tests
• Update the README

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Originally posted by @stefanotorresi at zfcampus/zf-mvc-auth#76

[weierophinney]

@stefanotorresi This looks fantastic! Any chance you can wrap up the lingering todo items soonish?

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Originally posted by @weierophinney at zfcampus/zf-mvc-auth#76 (comment)

[weierophinney]

@weierophinney been a bit busy lately, but I'll try to attend to this before the end of this week!

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Originally posted by @stefanotorresi at zfcampus/zf-mvc-auth#76 (comment)

[weierophinney]

@stefanotorresi I pulled this locally, rebased it off of current develop, and tried to push to your branch... but could not. So I did a PR for you: stefanotorresi/zf-mvc-auth#1

The tasks you have listed above are still incomplete, and, honestly, I'm unsure how to complete the first 2. If you would like to continue with this patch, please merge the PR I sent you, and push changes back to your branch when complete.

Thanks!

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Originally posted by @weierophinney at zfcampus/zf-mvc-auth#76 (comment)