[ticket/11334] Include functions.php and fix class name in tests

PHPBB3-11334
[ticket/11334] Expand functionality of helper->url()

Expanded the functionality of helper->url() to support all parameters of
append_sid() itself.

PHPBB3-11334
[ticket/11334] Move unit tests for helper->url() into own file

PHPBB3-11334
[ticket/11334] Use mocks instead of making parameters optional

PHPBB3-11334
[ticket/11334] Fix copyright year in test file

PHPBB3-11334
Merge pull request #6 from nickvergessen/ticket/imkingdavid/11334

ticket/imkingdavid/11334