CodingStyleTest: run testXHTML for each business template

 - run `testXHTML` on business templates "one by one"
 - fix all the problems with the currently tested business templates
 - because `erp5_ingestion` was containing some tests skin folder depending on other business templates and because I did not want to add dependencies to `erp5_ingestion` I moved the tests in `erp5_ingestion_test`.

/reviewed-on nexedi/erp5!989