Added a low pass filter before median filter
http://stackoverflow.com/questions/3377288/how-to-remove-gravity-factor-from-accelerometer-readings-in-android-3-axis-accel

I should probably use a number spinner on the graph view. Step detection
overcounts still, probably on the downward acceleration. I could
probably add a "lockout" period, in which steps aren't counted after a
step is registered.