Add templating options in the form

Created originally on Bitbucket by guewen (Guewen Baconnier)

Was already merged in Bitbucket before import, marked as merged by the import user

See https://github.com/OCA/reporting-engine/issues/121#issuecomment-291801829

And the companion pull-request for odoo's report_py3o: https://github.com/OCA/reporting-engine/pull/122