add an optional kill button which can be on the pause button pin or on a different pin
add to config
fix typos
Merge remote-tracking branch 'upstream/edge' into feature/kill-button
minor refactor of gcode dispatch
Merge pull request #538 from wolfmanjm/upstreamedge

add StepperMotor::get_last_milestone()
add P1.18, P1.20, P1.21, P1.23 as laser PWM pins
update config
Added P1.24, P1.26, P3.25, and P3.26 to Laser
Added P1.24, P1.26, P3.25, P3.26 to Laser config
Implement triffid hunters flush queue code in Conveyor
Change things that call ON_HALT to not take pause
ON_HALT will set a state in gcodedispatch to reject all incoming commands until M999
ON_HALT will flush block queue
Merge remote-tracking branch 'upstream/edge' into feature/kill-button

Conflicts:
	ConfigSamples/Smoothieboard/config
Merge branch 'feature/kill-button' into add/clear-block-queue

Conflicts:
	src/modules/communication/GcodeDispatch.cpp
	src/modules/communication/GcodeDispatch.h
clear limit triggered if no limit switches still triggered
Add halt status to panel and a way to clear it
ON_HALT aborts sd play file
clear killed flag on M999
fast flash play led when halted
can;t do anythng nasty on on_halt as it may be from interrupt
abort flushes block queue
leave player in halted state until M999
make flush queue on abort optional