Enhancement: Delete Cache button

### Impacted plugin

Super Cache

### What

Improve context function and wording of Delete Cache button

### How

Hello, thanks for a great plugin.

The Delete Cache button would be much more helpful if, like on the front-end, it worked in the context of Pages and Posts in the back-end please.

For example, if I look at a Page on the front-end, hover my mouse over the Delete Cache button, I can see it will only delete the cache for that page - that's quite handy because it's often not necessary to delete the entire cache which seems to be the button's function in all other cases.

Front-end `path=/page-slug/`

Back-end of same page, `path=/`

Would much like to see a drop-down with two options pleas:
- Delete entire cache
- Delete the cache of this page/post

It looks like there will need to be a special case made for the home page, since `path=/` seems to mean deleting the whole cache?

No file or test is named. Start by locating the Super Cache back-end Delete Cache button and comparing it with the front-end context behavior; verify separate whole-cache and page/post-cache actions, including the special case where the home-page path is `/`.

Written by the indexing model from the issue text.