Default choice for body format (auto/txt/html) in module's setup

Enhancement for issue #1

class/sribmcustommailinfo.class.php

@@ -368,9 +368,13 @@ class SRIBMCustomMailInfo extends CommonObject
             $this->subject = $template->topic;
             $this->body = $template->content;
             $this->addmaindocfile = $template->joinfiles;
+
             // By default, we don't send emails when the generated invoice is
             // still a draft.
             $this->active = $this->fac_rec_object->auto_validate;
+
+            // Retrieve the default body format from config.
+            $this->body_ishtml = $conf->global->SENDRECURRINGINVOICEBYMAIL_BODY_ISHTML_DEFAULT;
         }
 
         return 1;