editable description

[``* `#16988` editable description``](http://community.openproject.org/work_packages/16988)
Actually there isn't something like a work package textile path but a textile path with a context. Thus, I would rename this method to ``apiV3TextilePath`` first. Second, I would pass ``context`` so the implementation would become:
```JS
var textilePath = PathHelper.apiV3 + "/render/textile";
if (context) {
  textilePath += "?context=" + context;
}
return textilePath;
```