Cleanup of/ease backlight control
put screensaver check into separate function aswell, initialise doDim (makes else-branch unneccesary)
change ambiguous naming, rename dimming-check methods
reset dim state so backlight gets dimmed upon reload/reconnect again
set backlight state before drawing content (fixes empty display on undim on some hardware like imonlcd)
Merged branch 'backlight-control' - fully refactored and simplified backlight handling, no more separate dimming for screensaver and video/music playback

Originally submitted by theonlychriss via PR#3 - many thanks for taking on this!