[task/code-sniffer] Require code sniffer to pass on Travis CI.

PHPBB3-11980
[task/code-sniffer] Check phpBB/phpbb first. This is where new files go.

PHPBB3-11980
[task/code-sniffer] Reorganise .travis.yml

PHPBB3-11980
[task/code-sniffer] Cleanup code sniffer ruleset files.

PHPBB3-11980
Merge pull request #1835 from bantu/task/code-sniffer

[task/code-sniffer] Require PHP Code Sniffer to pass