flash led1 on gcode received, dimmed loops, led2 init done + main loop, led3 idle loop

trying to make more use of leds:

- led1 flashes when receiving gcodes (I mainly wanted *this*)
- led2+led3 are dimmed, they were too distracting for only showing idle action
- led3 flickers when actions are going on
- led2 used for end of init phase (on) and main idle loop (dimmed)
- led3 used for slow ticker idle loop

this could be implemented more generally (e.g. using a class Led), but I think this wouldn't be of much value until more uses come up.

--HG--
extra : source : 51a0b52e50ab596ad39f75d65ec742eb03bec58e