add parole to video players
flag the synapse with user.ui
temporary remove tumblerd from user.bg_high

tumblerd tends to eat all cpu when the media file is being written
(i.e. downloaded)
inherit user.ui flag of xfce4-panel
add tracker-store to user.idle, it eats cpu on some situations
20-single-user-desktop.lua: set memory.move_charge_at_immigrate = 3 for system essential cgroup