Rethink release cycle

[gilbertsoft]

Currently we have the problem with the new releases that the start page is updated before the download page or the old /json api is ready and this leads to questions by the users. The start page should be updated after everything else is ready and not before.

[gilbertsoft]

One solution could be to flag new releases to prevent showing them on the start page. The Darth scripts should check the various download links and perhaps also the version constant especially for the split tree packages for composer installs. After the checks have passed Darth reflags the release to be ready now and the start page is updated. The releases should not be visible public before this point also not in the /json and the new api. Then Darth checks again e.g. the json and the announcements are done after this point.

[gilbertsoft]

This should be solved now by various caching optimizations #369, #363, #337