src: Move brightness handling functionality into own module
Merge branch 'feat/brightness'
src: Move visual indication from pwm_modifyLdrBrightness2pwmStep() to user.c

This moves the visual indication to the user to user.c. Instead of only
toggling the PWM output in case a change in offset has been detected, this
makes also sure that the PWM output is toggled each time the appropriate
user command is received.
src: pwm: Introduce functionality to get status of pwm_is_on