Enhancement: Advanced Settings screen visual aids

### Impacted plugin

Super Cache

### What

Advanced Settings screen visual aids

### How

A visual border to group Advanced settings per update button would really help to understand that button will only update that section.

I went through the entire Advanced Settings page changing all the settings, hit one of the buttons, only to realise it lost the changes I made the to other sections of that page and I had to press each button independently for each section.

Also, Ajax update of options on the Advanced settings page would be a nice touch.

Review the Super Cache Advanced Settings screen and its per-section update behavior first. Confirm whether the intended work is visual grouping, Ajax updates, or both; done means settings in other sections are not lost and each section's update scope is clear.

Written by the indexing model from the issue text.