parser: sanitize HTML: allow 'disabled', 'start', 'type' and 'checked' attributes

This makes check box lists like the following snipped work:

- [X] Done
- [ ] not done

Further allow the start attr, sometimes generated for ordered lists.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/Parser.js

@@ -20,7 +20,7 @@ Ext.define('Proxmox.Markdown', {
 	    for (let i=node.attributes.length; i--;) {
 		const name = node.attributes[i].name;
 		// TODO: we may want to also disallow class and id attrs
-		if (!/^(class|id|name|href|src|alt|align|valign)$/i.test(name)) {
+		if (!/^(class|id|name|href|src|alt|align|valign|disabled|checked|start|type)$/i.test(name)) {
 		    node.attributes.removeNamedItem(name);
 		}
 	    }