[ticket/11336] Changes "leaders"-mode to "team"-mode and so in test-file

PHPBB3-11336 

This tickets changes the mode "leaders", which is used for the link "the team" to more accurate "team". To avoid confusing to future style-authors the related template-file was renamed, too. Which will be of course unattractive to all existing styles and style-authors, but it is the only consequent way. 

The link in the tests-file: \phpbb\tests\functional\memberlist_test.php was renamed, too. 

http://tracker.phpbb.com/browse/PHPBB3-11336