Set button type to link buttons

Otherwise they are triggered by the form of the dialog when using +Enter.

issue11193
review380271002
(grafted from 3aed6c2db5e3276977aa8a0d4178d9adce54306d)

--HG--
branch : 6.0

src/view/form.js

@@ -910,6 +910,7 @@ function eval_pyson(value){
             this.el = jQuery('<button/>', {
                 'class': this.class_ + ' btn btn-link',
                 'name': attributes.name,
+                'type': 'button',
             });
             if (attributes.icon) {
                 var img = jQuery('<img/>', {