Updating docker php version to 7.3 (#5462)
Updating docker php version to 7.3 (#5462)

Closes #5325
Docker image updated:

    updated php-cli to 7.3
    updated xdebug to 2.7.0RC2 (stable version rather than beta),
    added zip functionality so composer could install from dist rather than source
    added classmap-authoritative option to composer for extra performance
    added no-interaction option to composer as without .lock files we'll pull latest version matched by .json definition, therefore build can fail any time if there's an interactive update [which is rare, but happens]
Codeception/Codeception,Codeception/base,Codeception/base,Codeception/Codeception,Naktibalda/Codeception,Naktibalda/Codeception,Naktibalda/Codeception,Codeception/base