[FIX] web_enterprise: kanban_state_selection ie

On IE (from 9.0 up to at least IE EDGE 14) we have this behavior
for the method serializeToString of XMLSerializer:

> (new XMLSerializer()).serializeToString($('<b>"</b>')[0])
  '<b xmlns="http://www.w3.org/1999/xhtml">"</b>'
> (new XMLSerializer()).serializeToString($('<b>"</b>')[0].firstChild)
  '&quot;'

Whilst browser such as chromium or firefox have:

> (new XMLSerializer()).serializeToString($('<b>"</b>')[0])
  '<b xmlns="http://www.w3.org/1999/xhtml">"</b>'
> (new XMLSerializer()).serializeToString($('<b>"</b>')[0].firstChild)
  '"'

Hence for IE9 and over, if in a `<t t-extend/>` a `t-jquery`
sub-directive (without `t-operation`) is available, we can have
broken javascript if a " is transformed into an &quot; at a unfortunate
location.

This commit favour node.data over XMLSerializer serializeToString to
avoid the possibility of this issue when a text node is processed.

opw-727283

addons/web/static/lib/qweb/qweb2.js

@@ -120,12 +120,15 @@ var QWeb2 = {
                 }
                 return r.join('');
             } else {
+                // avoid XMLSerializer with text node for IE
+                if (node.nodeType == 3) {
+                    return node.data;
+                }
                 if (typeof XMLSerializer !== 'undefined') {
                     return (new XMLSerializer()).serializeToString(node);
                 } else {
                     switch(node.nodeType) {
                     case 1: return node.outerHTML;
-                    case 3: return node.data;
                     case 4: return '<![CDATA[' + node.data + ']]>';
                     case 8: return '<!-- ' + node.data + '-->';
                     }