To Quit Application
on Button click use this code :
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
startActivity(intent);
Try it..
To kill the complete app and remove it from Running
app list kill the app through its pid
(its nasty)... use this lines before above code.
int pid = android.os.Process.myPid();
android.os.Process.killProcess(pid);