Improve deprecated class migration (download mapping files)
We can use https://github.com/FriendsOfTYPO3/compatibility6/blob/master/Migrations/Code/ClassAliasMap.php instead of our current solution with copying the autoload file of TYPO3.
Instead PHPCS might download the file on first run and update it. This way we can also download https://github.com/FriendsOfTYPO3/compatibility7/blob/master/Migrations/Code/ClassAliasMap.php and are able to do that for each TYPO3 version.
The user does not have to do anything in that case.