Feature: add total for IO tab

[axet]

Hello!

iotop great utility for CPU usage. It shows total and per process usage. But switching to IO tab lack of total IO usage metric.

I guess top panel can be replaced with per device IO and total meter.

EDIT: per device

EDIT: Looks like iotop not showing correct values of bytes written to the disk. but biotop does. Would be nice to have '-a' accumulate mode.

https://github.com/iovisor/bcc/blob/master/tools/biotop_example.txt

[BenBE]

Adding totals for a process (sub)tree isn't as straight forward internally for htop, as the data structures used internally don't easily provide the necessary information to do this on-the-fly.

[dsseng]

Regarding totals: it would be really convenient to be able to sort by totals this way. Useful in case I want to figure out application (container, build activity, etc) causing most resource usage and select it all, not look it up after finding the most hungry process.