[Feature request] Add support for _NET_WM_PID and WM_CLIENT_MACHINE X properties in Xorg-window

[PRESFIL]

I don't know if the imv window had such a property before, but could you please add support for it to imv. They can be useful for working with xdotool and other programs for automating windows in a tiling environment. Specifically, I need them for swallowing function on xmonad-contrib (original DWM's swallow). sxiv also don't have this properties (may not be have out of the box), but PR are open. You can take it as a basis.

Thanks in advance.