add optional PowerBar

[nwg-piotr]

• added optional PowerBar icons below the application grid; for each button to appear, you need to pass a command in the argument, e.g.:

-pbexit 'hyprctl dispatch exit' -pblock 'nwg-lock' -pbpoweroff 'systemctl -i poweroff' -pbreboot 'systemctl reboot' -pbsleep 'systemctl suspend' -pbsize 48

The -pbsize argument determines the icon size; closes #111;

• added clearing status line on button left;
• fixed finding ~/.config/user-dirs.dirs file (necessary to search files in users home directory).