Make PrevWordsInfo have multiple words' information.

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

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

...m/android/inputmethod/latin/ContactsBinaryDictionary.java

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

.../com/android/inputmethod/latin/DictionaryFacilitator.java

...android/inputmethod/latin/ExpandableBinaryDictionary.java

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

...rc/com/android/inputmethod/latin/RichInputConnection.java

.../com/android/inputmethod/latin/inputlogic/InputLogic.java

...utmethod/latin/personalization/UserHistoryDictionary.java

...utmethod/latin/spellcheck/AndroidSpellCheckerSession.java

...latin/spellcheck/AndroidWordLevelSpellCheckerSession.java

...m/android/inputmethod/latin/utils/LanguageModelParam.java

...roid/inputmethod/latin/BinaryDictionaryDecayingTests.java

.../com/android/inputmethod/latin/BinaryDictionaryTests.java

...putmethod/latin/RichInputConnectionAndTextRangeTests.java

...m/android/inputmethod/latin/makedict/Ver4DictEncoder.java

...hod/latin/personalization/UserHistoryDictionaryTests.java