extended composer PSR4 for tests; added simple Store setup-test to check fix for #94

[k00ni]

This rather complex pull request contains some work for the test area to enable connection tests for ARC2_Store. I also implemented namespacing for the test area (therefore adaptions on the composer.json).

composer:

• splitted classmap to classmap and files to allow autoload-dev with psr-4. otherwise classes were loaded twice
• autoload-dev now cares about namespaces in the tests area

tests in general:

• extended bootstrap to load tests/config.php if available with custom DB credentials
• added ARC2_StoreTest.php with very basic connection test. this test hopefully covers the fix for #94

existing unit tests:

• only adaptions to enable namespace usage for existing test classes
• ARC2_getPreferredFormatTest needed a simple workaround to avoid "undefined index" warnings thrown by PHPUnit

[semsol]

Thank you!

[crism]

Thanks, @k00ni and @semsol!