Added alternate way of sending media key presses that allows volume key ...

...skip track to work
with Google Play Music.

This is the same function that the lockscreen uses to react to media key presses but
is called via reflection.

See the handleMediaKeyEvent function in:
https://android.googlesource.com/platform/frameworks/base.git/+/android-4.1.1_r1.1/policy/src/com/android/internal/policy/impl/KeyguardViewBase.java

I've tested this using several other media players (DoubleTwist, Pandora, etc) and it seems to work on all of them.

I tested this on my Nexus 4 running stock 3.4 (JWR66Y) with GravityBox and no other modules installed.