Add gesture input enable settings

java/res/values/strings.xml

java/res/xml/prefs.xml

...rc/com/android/inputmethod/keyboard/KeyboardSwitcher.java

java/src/com/android/inputmethod/keyboard/KeyboardView.java

...c/com/android/inputmethod/keyboard/LatinKeyboardView.java

.../src/com/android/inputmethod/keyboard/PointerTracker.java

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

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