Avoid polkit authentication in automated power actions

In all "System - On battery/Plugged in" options do not ask for authentication, setting polkit_interactive flag from new xfce_{consolekit,systemd}_suspend() and friends to FALSE.

"General - Buttons" options should set polkit_interactive = TRUE because are user started actions.

See
libxfce4util#21 (closed)
libxfce4util!39 (merged)
!42 (merged)