Add ability to invert the PIR Notify LED

[jmw6773]

I've added the option to invert the PIR notification LED at build time. It's default value is set to drive an LED through a Mosfet. If the LED is driven directly from the AVR/ESP's pin, INVERT_LED_NOTIFY should be set to true.

[1technophile]

Thanks for the PR!

On other code parts, I'm using a different method (see LED_RECEIVE_ON) by specifying if the ON status is at HIGH or LOW,
I think we should uniformize the method used, I have no bias for one or another method as long as they are easily understandable and the same.

[jmw6773]

@1technophile, I don't have a preference either. I made a change that I think matches what you are doing with LED_RECEIVE_ON, but I haven't tested it, so I converted this PR to a draft. I'll try to build and push to my OMG tonight to confirm it functionality.

[jmw6773]

My OMG has been stable with this change.

[1technophile]

Thanks