Add php unit tests on expense reports

htdocs/api/class/api.class.php

...s/core/modules/expensereport/doc/pdf_standard.modules.php

htdocs/expensereport/card.php

htdocs/expensereport/class/expensereport.class.php

test/phpunit/AllTests.php

test/phpunit/CommandeFournisseurTest.php

test/phpunit/ExpenseReportTest.php