Define VERSION and BUILD in bootstrap.php.

We should get rid of this and use these dynamic constants via DI in our classes.
Add abstract base TestCase class to populate later on.
Add test cases for ConfigManipulator::removeObsoleteConfigEntries().
Add test cases for ConfigManipulator::removeObsoleteRepositories().
Add test cases for ConfigManipulator::removeObsoleteRequires().
Add test cases for ConfigManipulator::removeObsoleteScripts().
Add test cases for ConfigManipulator::updateContaoVersion().