Timeline - Nested groups do not use `groupOrder`.

[frankisans]

ItemSet.prototype._orderGroups use grupOrder option to sort all the groups (top groups and nested groups) but then _orderNestedGroups get the nested groups without applying order.

Maybe its enough to change:

       var nestedGroups = this.groupsData.get({
          filter: function filter(nestedGroup) {
            return nestedGroup.nestedInGroup == groupId;
          }
        });

to force the order again when geting nested groups:

       var nestedGroups = this.groupsData.get({
          filter: function filter(nestedGroup) {
            return nestedGroup.nestedInGroup == groupId;
          },
          order: this.optios.groupOrder
        });

We can even define a specific option nestedGroupOrder for sorting nested groups and use groupOrder if it is not defined.

In terms of performance, the first ordering of _orderGroups could be optimized to not include nested groups.

[eanugent]

Thanks for posting this issue. I'm not able to get my nested groups to sort in any order other than by the id

[brichbe]

Relates to #2676