[ticket/11458] Search for permission language files in extensions

Extensions that add new permission masks only need to add a permission file in
the language folder of the extension. The file must start with 'permissions_'
eg 'permissions_blog.php'. The permission language file will be automatically
included when viewing/setting permissions.

PHPBB3-11458
[ticket/11458] We still auto add language files from the mods and acp
folders in the language directory, so we revert some changes here

PHPBB3-11458
[ticket/11458] Add functional test

Since there is no test method to include extension language files, a
functional test seems more appropriate.
We add a permission mask 'acl_u_foo' with translation found in extenion
'bar' and confirm that the permission language file 'permissions_foo.php'
from 'bar' was added by asserting that 'Can view foo' exists when viewing
user permissions in acp

PHPBB3-11458
[ticket/11458] Fix test

PHPBB-11458
[ticket/11458] Fix functional test again

Add 'u_foo' to phpbb_acl_options
Make sure extension and fixtures are added before running test

PHPBB3-11458
[ticket/11415] Move while loop from ext manager to acp_extensions.php

Now enable_step works as it's supposed to (do one step at a time) and
less refreshes are required for the user.

PHPBB3-11415
[ticket/11415] Move migrator to base extension class from ext.manager

PHPBB3-11415
[ticket/11415] Remove migrator dependency from extension manager

PHPBB3-11415
[ticket/11415] Make migrator/ext.manager dependencies of the base ext class

PHPBB3-11415
[ticket/11415] Fix ext.manager constructor in tests

PHPBB3-11415
[ticket/11458] Use helper to create/move/delete directories/files

PHPBB3-11458
[ticket/11458] Use finder to get all permission language files

PHPBB3-11458
[ticket/11415] Create function in finder find_from_extension

PHPBB3-11415
[ticket/11415] Send the extension base the finder rather than the manager

PHPBB3-11415
[ticket/11458] Update functional test

Show that the phpbb permission lanuage file is being included

PHPBB3-11458
[ticket/11542] Add unit tests for language_select()

PHPBB3-11542
[ticket/11544] Add admin_login() method to 3.0 functional test case

This method is needed in order to be able to properly test acp functions.

PHPBB3-11544
[ticket/11415] Add test for find_from_extension()

PHPBB3-11415
[ticket/11542] Add lang_english_name to fixture

PHPBB3-11542
[ticket/11542] Add non-existing default value for language select

PHPBB3-11542