Reorganize SoundPool and JetPlayer code to be ready for the
creation of libmedia_native.
Split SoundPool between libsoundpool (JNI) and libmedia(sound pool implementation).
Remove dependencies on nativehelper/jni.h from JetPlayer.
Change-Id: I130c6014173b714329929dd82c5dfb70b757a610
SoundPool itself also creates a thread, which was called "SoundPoolThread", unrelated to the SoundPoolThread class. The SoundPoolThread class then created an unnamed thread, which showed up as "android:unnamed_thread". That's confusing, so this change renames the SoundPool thread to "SoundPool" and then names the SoundPoolThread thread as "SoundPoolThread". Say that ten times fast :)
Change-Id: I67b7e644a30c94b6eda44bf970764a52a1c2958b