Fix and Enhance Resource Groups Functionality

[smg6511]

What does it do?

Fix the parsing of differing node id formats to allow moving and copying of Resources between Resource Groups.

Along with fixing the original issue, this solution adds the ability to copy a Resource from one group into another by use of a modifier key (opt/alt - click) before/while dragging. New language in the panel's main description has been added to make this clear to users.

Why is it needed?

There was no group to group functionality. Attempting to move a Resource between groups would result in nothing happening and/or a endless progress dialog box.

How to test

Go to the Resource Groups editing panel (manager/?a=security/resourcegroup) and ensure the following works:

• Moving Resources from the right Contexts tree into one or more groups (this is unchanged)
• Moving a Resource from one group to another (drag drop without modifier key)
• Copying a Resource from one group to another (opt/alt - click - drag drop)
• The create and update windows; there's no new functionality here, just some code clean ups and little nuances fixed (such as the field error message shown when the group name is not specified)

Related issue(s)/PR(s)

Resolves #16274 for MODX 3.x.