Sulu Release 1.5.20 & 1.6.24

The first release in the new year is a rather small one, but allows to run Sulu 1.6 with the latest versions of Symfony and PHP 7.3. Sadly we had to realize that it is not possible to make Sulu 1.5 compatible with PHP 7.3, because we would have to update from Symfony 2 to Symfony 3, which would introduce quite a few BC breaks. So if you want to run Sulu on PHP 7.3 there is no way around an update to Sulu 1.6.

In addition to that the XML files containing the image formats can now be empty. We did this because this way it was possible to add an empty image formats file to sulu-minimal, which hopefully makes it easier to start a new project.