Rationalize tests and examples

GaudiExamples was meant to be a place where to keep example code, but it slowly turned into a place where to store internal integration tests, including the tests to ensure that we preserve backward compatibility with old ways of doing things.

This is counterproductive because we do not have anymore a clear way of promoting new practices as they are mixed with obsolete practices in the same directories.

I believe we should rename GaudiExamples in something like GaudiTests and start a new GaudiExamples where we only keep actual (up-to-date) examples.