Add a settings to change the sound effect volume

java/res/layout/sound_effect_volume_dialog.xml

java/res/values/strings.xml

java/res/xml/prefs.xml

java/src/com/android/inputmethod/latin/LatinIME.java

java/src/com/android/inputmethod/latin/Settings.java

java/src/com/android/inputmethod/latin/Utils.java