Mer/Blueprints/Backlight behaviour

System active -> System idle -> System inactive
 * Global properties in use:
 * Seconds since last input (SSLI)
 * System state (SS: Active, Idle, Inactive)


 * Gconf2 settings:
 * Backlight level while system active (Active Backlight Value)
 * Backlight level when display dimmed (Dimmed Backlight Value
 * Seconds idle before making display dimmed (Seconds To Dim)
 * Boolean value as if to keep backlight lit (Stay Lit)
 * Seconds idle before turning off display (Seconds To Turn Off)


 * HAL methods:
 * LaptopPanel/SetBrightness


 * Event-Reactions:
 * If ABV modified, and SS = Active, SetBrightness to ABV
 * If ADV modified, and SS = Idle, SetBrightness to ADV
 * If STD > SSLI, set SS to Idle unless SL
 * If SSLI < STD, set SS to Active
 * If STTO > SSLI, set SS to Inactive unless SL
 * If SS modified to Idle, SetBrightness to ADV
 * If SS modified to Active, SetBrightness to ABV
 * If SS modified to Inactive, SetBrightness to 0, turn off screen