Add preliminary graphics of sliding key input preview

java/res/values/attrs.xml

java/res/values/colors.xml

java/res/values/config.xml

java/res/values/strings.xml

java/res/values/styles.xml

java/res/xml/prefs.xml

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

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

...inputmethod/keyboard/internal/SlidingKeyInputPreview.java

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

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

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