also show the installation source for installed condidates.
change everything to use cce (our own edition of composer).
url decode version to allow ">=" and "<=" being used again in contao context.
keep track of already seen versions when fetching from multiple repositories
to ensure each version is only mentioned once. Before, the installed version
was mentioned twice, as it originated from the local repository and the
remote one.
make release date comparison optional and not raise a fatal exception.