[ticket/11568] Use static calls for static methods

PHPBB3-11568
[ticket/11568] Invert logic for asserting the response

PHPBB3-11568
[ticket/11568] Add comma at end of array key-value couple

PHPBB3-11568
[ticket/11568] Split status code and html debug assertion into two methods

PHPBB3-11568
Merge branch 'ticket/11568' into ticket/11568-develop

* ticket/11568:
  [ticket/11568] Split status code and html debug assertion into two methods
  [ticket/11568] Add comma at end of array key-value couple
  [ticket/11568] Invert logic for asserting the response
  [ticket/11568] Use static calls for static methods

Conflicts:
	tests/test_framework/phpbb_functional_test_case.php