Make sure main repository's src/ is PSR-4 compatible

[ek9]

From the old structure, some of the extensions still have src folders. This requires us defining multiple different paths in composer.json. Instead, I suggest to make sure that all patch in src directory (of BehatSpec is PSR-4 compatible).

[ek9]

This is required for #27 as otherwise we cannot properly configure PhpSpec and other extension tests to be run in the main repo.