Drop zend loader, module loader and autoloader provider features.

[weierophinney]

Composer has became a de-facto standard for managing dependencies and autoloading, Zend Framework itself distributes and manages its dependencies via composer. That makes Composer virtually guaranteed to be present for any application.

This PR drops autoloader support in zend-modulemanager in favor of composer autoloader.

This change opens a way for more Module Manager improvements to follow.

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Originally posted by @Xerkus at zendframework/zend-modulemanager#78

[samsonasik]

I've created PR #12 for it.