Add support for qweb-txt-csv

Thanks to Graeme Gellatly for his suggestion to implement it this way, so that other qweb-txt-* can be easily added with proper filename extension

report_qweb_txt/models/ir_actions_report_xml.py

@@ -8,12 +8,21 @@ from odoo import api, fields, models
 class IrActionsReportXml(models.Model):
     _inherit = 'ir.actions.report.xml'
 
-    report_type = fields.Selection(selection_add=[('qweb-txt', 'Text')])
+    report_type = fields.Selection(selection_add=[
+        ('qweb-txt', 'Text'),
+        ('qweb-txt-csv', 'CSV'),
+        ])
 
     @api.model
     def render_report(self, res_ids, name, data):
-        if data.get('report_type') == 'qweb-txt':
-            return self.env['report'].get_html(res_ids, name, data=data), 'txt'
+        if (
+                data.get('report_type') and
+                data.get('report_type').startswith('qweb-txt')):
+            ext = data['report_type'].split('-')[-1]
+            # That way, you can easily add qweb-txt-zpl' or others
+            # without inheriting this method (you just need to do the
+            # selection_add on the field 'report_type')
+            return self.env['report'].get_html(res_ids, name, data=data), ext
         else:
             return super(IrActionsReportXml, self).render_report(
                 res_ids, name, data)