Improve memory displays

[kjbracey2]

Separate out cache memory from the memory displays, avoiding confusion.

In the router status, "free" is changed from being MemFree to being (MemFree + Cached - Shmem + SReclaimable + Buffers), so it includes probably-claimable memory. This is equivalent to htop's cache + buffers + free. "Used" is then physical total minus that, equivalent to htop's used + shared, plus the reserved memory not counted in Linux's total.

In the Tools, existing fields are left as-is, but new "Used" and "Available" rows are added. "Used" is equivalent to htop's used + shared, so matches the router status display, except that we're not including reserved memory. "Available" is the kernel's MemAvailable value - a good high-level space available indication.

Follows discussion at https://www.snbforums.com/threads/ax88u-high-ram-usage-maybe.76650/

[kjbracey2]

There are still people getting confused by this: https://www.snbforums.com/threads/fix-this-bug-pls-big-file-size-copy-and-the-memory-getting-full-ver-386-4.76947/

[JackMerlin]

awesome

[Eldenroot]

Is this included?