Migration of account_journal_report_xls to 8.0

* Corrected Pylint Warnings
* Added tests
* Added translation template
* Fixed a Many2many bug: https://github.com/odoo/odoo/issues/3751
I totally agree but I am not the author of the module and this PR is only a migration to v8, not a refactoring. IMO this point should have been raised and adressed before the inclusion of this module. (same remark for the other comments below)