Update ProductCallbacks.php

Typo in #421
Require "contao/core" instead of non existing package "contao".
Only replace contao-legacy/isotope in self.version.
Starting 1.4.8 hotfix branch
Merge branch 'master' of https://github.com/tristanlins/core into hotfix/1.4.8
Improved composer.json
Merge branch 'patch-1' of https://github.com/joke1/core into hotfix/1.4.8
Fixed edge case SQL issue in rules module (#771)
Generated PDF did not search the shop config folder in the back end (#534)
Try to retain line breaks when converting HTML to text (#880)
Updated changelog
Merge branch 'hotfix/1.4.8'