MDL-79871 qtype_ordering: Further changes for readability

Part of: MDL-79863
- Reduce usage of jQuery to only a couple of variables. These are left as is due to how heavy the usage is and how the base dnd seems to assume jQuery objects here and there.
- Templated the proxy string so we dont have to pull it in and replace tokens on the fly.
- Moved around functionality a bit to make for more concise reading and obvious delegation of responsibility