Separate TimeKeeper from ForgettingCurveUtils.

native/jni/Android.mk

native/jni/src/suggest/core/dictionary/dictionary.cpp

...rc/suggest/policyimpl/dictionary/header/header_policy.cpp

.../src/suggest/policyimpl/dictionary/header/header_policy.h

...ionary/structure/v4/ver4_patricia_trie_writing_helper.cpp

...t/policyimpl/dictionary/utils/dict_file_writing_utils.cpp

...st/policyimpl/dictionary/utils/forgetting_curve_utils.cpp

...gest/policyimpl/dictionary/utils/forgetting_curve_utils.h

native/jni/src/utils/time_keeper.cpp

native/jni/src/utils/time_keeper.h