Option to display swap usage as a percentage, not as size

[HubKing]

Has this issue been covered in the Wiki?

• [X] I have read the Wiki and my issue is not covered.

Is there an existing issue reported already?

• [X] I have searched the existing issues, it does not exist.

Describe the new feature you would like

It seems that unlike physical memory usage, Swap cannot be displayed as a percentage but only as size (e.g., 123.4 MB). In Gnome's System Monitor, both physical and swap are displayed in the same manner (size and percentage), so it should be possible to display the value as a percentage.