Updating Items for a Graph Template may be slow on larger systems

[TheWitness]

Describe the bug

When making small modifications to a Graph Template on very large systems with tens of thousands of graph, the process can take a long time to complete in the orders of tens of minutes, which causes web server and proxy timeouts.

To Reproduce

Steps to reproduce the behavior:

1. Edit a Graph Template with 50k Graphs

2. Edit any Graph Item

3. Press Save

4. Go get a coffee

5. Beat the cat

6. Read War and Peace

7. Come back and find that the save never finished

Expected behavior

Cacti should save Templates in an efficient manner.

[TheWitness]

Still have one case that is not addressed, and there are still corner cases where performance is not good.

[TheWitness]

I'm going to mark this resolved, though there is still room for improvement. It's must faster now anyway.