pipicpowerd.c add configuration file

The file /etc/pipicpowerd_config is now read at the start up. The following
parameters can be set from the configuration file

LOGLEVEL 0-4  4=only warnings, 0=debug
VOLTINT       voltage reading interval [s]
LOWBATTERY    minimum battery level before power down
PICYCLE       PIC counter cycle [s]
BUTTONINT     button reading interval [s]
CONFDELAY     waiting time for confirmation button press for shutdown [s]
PWRDOWN       delay to power down in PIC counter cycles
SETTIME       if '1' set system time from PIC counter