Added Alice loader to LoadFixturesCommand.

Command doctrine:fixtures:load loading Doctrine\Fixtures and Alice\Fixtures.

Command is tested, but for testing Doctrine\Fixtures is need for mocks, so I've tested only Alice\Fixtures.

Enabled injecting to LoadFixturesCommand.php in extension.
Added method for loading all alice files into Alice\Loader.php.
Without `\` as in the rest of file.