Feature/ui dashboard setting

* Dashboard endpoints [Namespace aware]
* User Settings endpoints

The PR does not contain (will be added in future):
* ACLClient integration (Dashboard Read/Write access check)
* Namespace deletion hook --> Delete all dashboards belonging to that namespace when it is deleted.
so far I've seen "setting", "property", "attribute" (?). So which one is it? Also, for dashboard API, we don't change individual property. We store dashboard config as the whole json string, right?