Charge thresholds not supported

Hi there, I hope this is a small fix. I could make a pull request for it but I need your approval first.

Basically I am getting this error

Jan 07 16:07:56 asus org_kde_powerdevil[2607]: Warning from helper: Failed to open "/sys/class/power_supply/BAT0/charge_start_threshold" for reading
Jan 07 16:07:56 asus org_kde_powerdevil[2607]: Warning from helper: Failed to open "/sys/class/power_supply/BAT0/charge_stop_threshold" for reading
Jan 07 16:07:56 asus org_kde_powerdevil[2607]: org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds not supported"

However Charge threshold is supported on my linux machine but file name is different. It's called:

/sys/class/power_supply/BAT0/charge_control_end_threshold

which is a read/write file

so you can do

echo 80 > /sys/class/power_supply/BAT0/charge_control_end_threshold
cat /sys/class/power_supply/BAT0/charge_control_end_threshold