RFE: ps output: add section on top users of threads

[ryran]

Mockup:

PS CHECK
  Total number of threads/processes:
    910 / 258
  Top thread-spawning users:
    USER     PIDS   THREADS
    rsaw     82     457
    root     144    331
    gdm      26     103
  Top users of CPU & MEM:
    USER     %CPU   %MEM   RSS
    rsaw     10.5%  55.9%  4.50 GiB
    gdm      0.1%   3.8%   0.39 GiB
    root     0.0%   4.9%   0.53 GiB
    polkitd  0.0%   0.2%   0.02 GiB
    geoclue  0.0%   0.2%   0.02 GiB

Great idea mkolbas.