Change repository layout to Maven Standard Directory Layout

This does only affect files in `src/test` as there are yet some places where we don't "stick to the standard".

As a followup, some tests need fixing as they relied on certain filesystem paths which have now been changed.

Note: Commit 46bc090 could be extracted as it is a general bugfix for the test.

What has changed (summary):
* moved `src/test/resources/*.ini` --> `src/test/config/unittest/*.ini`
* moved all files != `*.php` in `src/test/php` to `src/test/resources/`
* removed override settings in `pom.xml`, adapted `.travis.yml`
* added `src/test/resources/` into `core.pth` (for `lang.ResourceProvider` to pick up the resources)