s/insensivite/insensitive

s/referene/reference

s/unavailabe/unavailable

s/validing/validating

* Unify templated files
  A lot of files are identical throughout the different packages.
  This is the base for unifying them for easier handling.
* Adjust tests path
  Some packages use 'tests' as tests directory, while other use 'Tests'. The reference in phpunit.xml.dist is adjusted accordingly.
* Build: Ignore PHP 5.4 and 5.5
  The images used for tests with these versions have problems with using composer (giving curl error 60), so they are removed for now, until a solution is found.
* Build: Introducing loose and strict code style check
  As some packages irreversibly violate our code style by using underscores in variable and method names, the loose check will let names with underscore pass. This check must pass. The strict check is applied without any exceptions, but allowed to fail, so we still get informed about these violations.
* Build: Check for PHP 8.1 compatibility
  Since the CMS has expressed a need for PHP 8.1 compatible versions of the packages from Framework 1, compatibility should also be tested.
* Tests: Don't use phpunit.xml to provide PHP values
  The phpunit.xml should only specify values that are required by the test environment. Everything that the tests themselves require should be made available via bootstrap.php.
* Tests: Provide separate tests for PHP < 7.1 and PHP 7.1+