Memory [Graph] meter - Don't include "cache" in the bar height

[dasKeks28]

When displaying the memory meter as graph, the height of the graph bars includes used, buffers and cache and thus is relative to (MemTotal - MemFree).

When displaying as [Bar] there are different colors for the different memory usages, unfortunately this is not available for the graph meter. Therefore the graph does not show the actually (un)available memory.

Can we have this changed to only display the reserved memory, so used + buffers i.e. (MemTotal - MemAvailable) as bar height?

[eworm-de]

Would be nice to have #129 for this... Colors are available for graphical memory meter there.

[dasKeks28]

That would be great, too.

EDIT: The limited precision caused by only having 4 characters that can be colored is somewhat problematic, though.

[fasterit]

Resolved via #1540