[feature/auth-refactor] Have a base auth class

PHPBB3-9734
[feature/auth-refactor] Prevent fatal error in php < 5.3.23

PHPBB3-9734
[feature/auth-refactor] Remove implements on classes extending base

PHPBB3-9734
[feature/auth-refactor] Change 'must' to 'should'

PHPBB3-9734
[feature/auth-refactor] Code style fix for doc blocks

PHPBB3-9734
[feature/auth-refactor] Remove full stop

PHPBB3-9734
[feature/auth-refactor] Check that providers implement auth interface

PHPBB3-9734
[feature/auth-refactor] Remove invalid providers from acp select

PHPBB3-9734
[feature/auth-refactor] Fix typo

PHPBB3-9734
[feature/auth-refactor] Fix style issue

PHPBB3-9734
[feature/auth-refactor] Test that acp_board excludes invalid providers

PHPBB3-9734
[feature/auth-refactor] Move test classes into separate directory

PHPBB3-9734
[feature/auth-refactor] Code style change

PHPBB3-9734
[feature/auth-refactor] Test selecting invalid provider as well

PHPBB3-9734
[feature/auth-refactor] DataProvider for acp_board test

PHPBB3-9734
[feature/auth-refactor] Changes

PHPBB3-9734
[feature/auth-refactor] Add parent::setUp() in setUp()

PHPBB3-9734
Merge pull request #1515 from Hardolaf/feature/auth-refactor

[feature/auth-refactor] Use a base class for all authentication providers