NoMan/SysUI: Clear LEDs only when entering the shade

Don't clear notification LEDs when seeing notifications on the
lockscreen.

Also fix a bug where the LED didn't continue flashing after
the screen turned off.

For devices with doze capability, ensure that the LED continuing
to flash after screen off doesn't cause an immediate pulses, but
delay the first pulse by 10s.

Bug: 15449039
Change-Id: Id34d51a2c91ceaf069e49add1ab690bb855f9638