inga_demos: changed LEDs to use leds_toggle()

leds_invert() was removed from LED driver and also the wrong approach to toggle LEDs.
inga_demo: use LED defines for easier understanding
inga_demo: show how 'bitwise or' can be used to handle multiple LEDs at
once
Merge pull request #12 from yschroeder/pull-req/leds_toggle

Changed INGA examples for LED usage