When sorting Data Sources, missing index causes unnecessary delays

[cigamit]

Describe the bug
On very large Cacti installs, the Data Sources page may be slow due to a missing index on the name_cache column

To Reproduce
Steps to reproduce the behavior:

1. Go to Data Source apge
2. Sort by the ID column, measure time
3. Sort by the Name column, measure time
4. Not the increase in time

Expected behavior
Behavior should be consistent between sorted columns

[netniV]

@TheWitness may need to check for that on Thresholds too where it was added recently.