Re-adding autoplay on heatset insert

I am grateful the continued work you have done on Vanilla.  Thank you for not letting a great project die.    The one key feature I wish it still had was the play on headset insert feature which was removed a year ago.  Judging from comments other users have posted, I am not the only one who found it incredibly handy.  While I did compile and install adrian-bl/vanilla-headphone-detector, this is not provided through F-Droid and it does not seem necessary to have it as a separate app in the first place.  

With that being said, I have mangled together the code form the two repo's to be a single package under Vanilla.  I have tested this on my Kitkat device.