Signed v3.0.0 release

Tagging 2.0.0

Initial commit

Move TestingAccessWrapper from MediaWiki into a separate library.

Code was taken from the following files in
MediaWiki commit 82d3ab93ad15a34089ab81a9a9d62ecd3d2e48ec:
- tests/phpunit/includes/TestingAccessWrapper.php
- tests/phpunit/includes/TestingAccessWrapperTest.php
- tests/phpunit/data/helpers/WellProtectedClass.php

Contributors to those files, per git shortlog:
     2  Adam Roses Wight <awight@wikimedia.org>
     1  Brad Jorsch <bjorsch@wikimedia.org>
     1  Gergő Tisza <gtisza@wikimedia.org>

Change-Id: I387dd09b9a1c995f2e535c0b112997f3a72d2126
Depends-On: I877ec9b988019d99c8a1734c3ec1b7e3f8684a47