let HDDTEMP controled by settings

currently HDD Temp is always showed.

make it controled by "display-hdd-temp"

Signed-off-by: zhangn1985 <zhangn1985@gmail.com>
change the coding style in extension.js

change coding style
change code logic
add comments

Signed-off-by: zhangn1985 <zhangn1985@gmail.com>