Support additional proximity characters

java/res/values-en/additional-proximitychars.xml

java/res/values/additional-proximitychars.xml

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

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

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

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

native/src/correction.cpp

native/src/correction.h

native/src/defines.h

native/src/proximity_info.cpp

native/src/proximity_info.h